Back when I started collecting comic-books in 1976(ish), comic-books were only produced in monthly or bi-monthly serialized form. If you missed an issue, your collection was going to have a gap in it. There were few, if any, direct-market comic-book shops back then, so you could only buy your issues on the news stand. And news stands did not hold back-issues -- unsold comics were returned to the publisher for credit (so that the news stand was not on the hook for items that didn't sell). Back then, in other words, reading every issue in a comic-book series required you to buy every issue as it came out. This was a significant challenge, and I don't think I had a single friend with a complete collection that lasted more than a handful of issues. For example, I got interested in Rom: Spaceknight on issue #24. I picked up #26 and #28 (but missed the odd issues for some reason), and then finally with #30 was devoted enough to the series that I picked up every single issue from #30 to #60 or so. But although I wanted to read the earlier stories, back then, there was no good way of obtaining them.
By the 1980s, direct-market shops had started to appear in more locations, and it became possible to obtain some older back-issues. I was able to buy a few of the Rom issues between #1 and #23 (though only about a third of them). Still at this time, if one wanted to read every story in a series, one had to buy the individual issues. Thus, the back-issues made this possible, as it had not been before the 1980s, but it was still extremely difficult.
Finally, by the 1990s, the comic-book companies started putting out bound, collected editions of older issues, either as paperbacks or (very rarely) hardcovers. The most common way for them to do this is with the "trade paperback," or "TPB", which is a softcover collection. The first trade paperback I ever remember buying was the Batman story, "A Death in the Family" (the original one, wherein Jason Todd was murdered by the Joker). I had not been wise enough to pull the trigger on the individual issues, believing that the whole thing was just hype, but when I heard that the story was excellent, I bought the TPB. This was typical of the trend in the 1990s, which was for the companies to collect significant or important storylines (such as the "Great Darkness Saga" from the Legion of Super-Heroes), or else storylines that had sold out in their regular print run, but which were still in demand by the readers ("A Death in the Family" being a good example).
Since the turn of the century, however, comic-book companies have started to put out far more TPBs. They discovered that TPBs are quite popular with many readers, because the TPB provides the reader with a number of advantages. First, TPBs usually collect a complete, self-contained storyline (aka. an "arc"), and can be read almost as a stand-alone. There is no need to track down every issue in the story. Second, TPBs often provide the reader with significant cost savings (a typical 6-issue arc at $3.99 a pop is $24, but most TPBs collecting six issues are priced at around $19.99). Third, TPBs because they have no value beyond the cover price (they are always reprints, and thus rarely worth anything to serious collectors), make it unnecessary to bother with the usual steps one must take to store and protect individual comics (mylar bags, backing boards, and the like). And finally, with their square, stiff spines, TPBs can be stored on a bookshelf with no risk of them bending or warping, which saves tons of space over the typical "long boxes" in which individual issues are stored.
For all these reasons, the TPB format has become increasingly popular, and I am certainly a fan of it. When a friend recommended the Sandman series, for example, it was already over, and each first-print back-issue was rare and valuable. Trying to buy the series as 75 individually priced comics would have cost a small fortune. The TPBs, however, were readily available, and probably cost a tenth of what the individual back-issues would have cost me. Thus, I quickly got on board the TPB bandwagon. Many readers feel the same way, and the comic companies have responded. Most writers now seem to "write for the trades" -- meaning that, since TPBs normally collect 4-8 issues, averaging around 6, most story arcs are written to that length (again, averaging around 6 issues), so that as soon as the arc is done, it can be bound as a collection and sold to those who prefer the TPB format.
Reading through comments on the Google+ Comic-Book Community, I have noticed that many people now only buy TPBs. They have to wait a bit to get the story, but they are willing to do that for the convenience of all the advantages listed above.
Today, I ask whether "waiting for the TPB" is dangerous, from the standpoint of a character or a series that you like to read. How can it be dangerous? you ask. My answer is that, in general, the comic-book companies seem to respond primarily to the sales of individual issues on the stands. Although I'm sure they are gratified when people buy the TPB collection, the TPB is usually published 6 months after the storyline completes, and since most stories are 6 issues long, that means a TPB will be published a year after the first issue in the arc appeared. That's a long time in the comic publishing world.
To see why waiting for the trade is dangerous, let's use the example of a current disaster series for DC (in terms of sales): Katana. The series debuted in February, selling 27,000 print copies the first month. By April, sales had dropped to 16,000, and by June it was limping along at 13,000. We also know from recent history that +DC Comics tends to cancel comic-book series that sell less than 20,000 issues per month. Now, maybe nobody likes Katana and that's why her sales are dropping. But let's imagine for a moment that the 13,000+ people who stopped buying it between issues 1 and 5, decided they liked it, but wanted to "wait for the trade." The TPB of the first arc won't come out until January 2014 or so. Meantime, Katana is in the "cancellation red zone" for months. The risk here is that DC will see slumping sales and cancel the series in July or August, long before the TPB ever comes out. Even if they put out a TPB of the first story arc in January (which they might not bother to do for a comic that doesn't sell well), and even if the TPB sells like gangbusters, by then, the series may already be canceled and it may be too late to do anything about it.
Don't think it can happen? It already has. Threshold is being canceled as of issue 8. Hawk and Dove was as well. Justice League International lasted just 1 year. All of these books were canceled before the first story arc could be collected into a TPB, published, and the sales figures for the TPB could be tallied.
This is why I believe that, if you truly like a comic-book enough to buy it regularly and keep reading it, it's very dangerous to "wait for the trades." I do understand the convenience, and when buying back-issues, I definitely prefer TPBs to individual issues in most cases -- for the lower cost, the lower maintenance, and the convenience. But if you like a comic and you want it to keep being published, the sales that indicate your feelings won't be tallied until months after the issues are published, and you risk your favorite series being canceled. The only way to be sure the companies know you are on board with their title is to buy it every month, as it comes out -- and better yet, put it on your pull list, so the store knows to order another copy of it. Yes, it is less convenient than "waiting for the trade," but is the TPB worth risking the series being canceled? To me, the answer is "no."
I am not, of course, trying to tell anyone what to do. If you prefer trades, that's fine. But you should be aware of the risk you're taking with any series you truly enjoy... Because you may just be one person, but if everyone decides to "wait for the trade," not just you, then the sales may slump so badly the title gets canceled, even though thousands of people actually would buy it next year when the TPB comes out. So... as with all things... caveat emptor.