I've never been in an campaign scheduled that tightly, though, so I can't really comment.
Well, I'll take my own group as an example. We're playing classic Deadlands - no classes, no levels. We could, in theory, play the campaign forever.
For a long time, the PCs have been (wisely) actively avoiding the Big Bad Evil People, because the BBEP would squish inexperienced characters like bugs. The PCs concentrated on foiling plans out on the outskirts, near their ends, rather than going for the heart. But, it has been a couple of years, now. They feel they're ready to take on the Bad People (they're correct - they can do it, if they're smart).
So, I'm looking at the point where they will resolve the major plot threads in the foreseeable future. And I have to ask myself, "Do I add more plot threads, or do I allow these to resolve, and then do something else with the group?" Every good story has a beginning, a middle, and an end, so I'm likely to choose to let the plots resolve, and close the campaign off. I then have to consider when I start putting real thought into my next game. If it is a year out, I don't need to worry about it now. If it is six months out, I ought to start looking at rulebooks for systems I've found intriguing.
This isn't "tightly scheduled". It is very vaguely scheduled, at best. But I have to think about it now, if I don't want months of non-play for my group in the future.