I actually don't see whats wrong with it?
Once it hits 200 or just above a new thread is created and usually linked inside the old one, so its no more different than changing page.

Well, I just posted it above :
All that having cutoff points make is :
- greatly stifle any discussion that was going on at that point
- make quoting messages from before the cut a pain
- promote offtopics discussion about the event itself
- make it THAT much harder to find information since you need to hunt all the tiny pieces and search inside instead of searching once (hint, there's a tool called "Search inside this thread" that doesn't follow through other chunks)
- litter the forum with locked threads
- make the "Follow this topic" tool rather ineffective
And I added that one later :
- makes you lose all poll progress when the thread included one