This does not happen with villagers or cows etc. Only with hostile mobs. I always try to play with hostile mobs, but my game goes extremely laggy. I can only play on Peaceful mode.
Minecraft extremely slow when there are hostile mobs around?
Atom Reed
Villagers and mobs don't have a smart AI, while the hostiles… Still don't have a smart AI but it does something, in most case you processor just stinks.
Radu