The problem with extremely well defined limits is that those who choose to be assholes will ride up to that line and push it constantly. Then use the defense "

The problem with extremely well defined limits is that those who choose to be assholes will ride up to that line and push it constantly. Then use the defense "the rules don't say I can't call you a butthead", so the rules get updated then they push some more and the cycle repeats. With fuzzier boundaries if someone is being an ass you can kick them the first time. This does of course mean you need a decent set of moderators and an appeals process to prevent people power tripping.