Here are the things we limit for server stability.
Speed and Timer hacks are limited to 96 blocks per second. Excessive speed can lag the entire server, so we had to limit this.
Flight Hacking has caused a few major bypasses for speed hacks, and also ruins a few aspects of real vanilla gameplay (like PvP). In order to fully prevent flight hacking, we also have to disable AntiHunger and NoFall exploits.
We have a special command to limit spammers. Nobody likes them. If you encounter an annoying spammer, you can vote mute them with /vm. 40% of the server population also has to vote for the person to be muted for an hour.