When you give changes (via Commands) to enitties (move them or change their NBT constantly) with a fastclock. The game starts to lag EXTREMELY compared to older Versions of the game. This ruins a lot of things that were previosly possible with commands.
Fact is that is lags even though CPU Usage and RAM Usage on the Server are really low! It even crashes the Server sometimes.
1.place about 50 Villagers
2.Blue commandblock with /tp @e[type=!Player] ~ ~.5 ~.1