Random tick speeds of around 1000 and up cause a lot of lag.
Comments 4
Lag when things are actually happening is normal, but the lag happens even when there aren't any blocks affected by the random updates.
The lag is very apparent when shooting arrows, I started noticing it at around 5000 random tick speed
Confirmed, but likely intended/unfixable since crop growing/fire spreading etc all happen at an extremely fast pace. (try growing crops/setting fire to flammable blocks/melting ice/allowing leaves to decay and you will see what I mean 🙂)
http://minecraft.gamepedia.com/Commands#gamerule