Well, one example is a "random" thread, in which one person starts it and posts something random, then other people post until it reaches 100, then a mod/admin has to manually close it, which can get to be a hassle. The purpose of this limit in particular is just for fun, because everyone likes to be the one to start the next random thread.
Yeah, I realize this example is silly, but there can be other uses for this feature.
Any ideas?
Thanks.
Edit: Er, I suppose either limiting the pages or the post # (the latter might be easier) would work just the same.