when do i use maim or rip

i know at 5 combo points but when shoulld i use it and what classes i should use it on?
Use Rip on everything, unless its health is low enough that Ferocious Bite will finish it with 5CP.

Maim is useful when you know the target is winding up for big damage and you want to interrupt it, or you have Rake/Rip bleeds on it and 5 sec of interrupt will let it bleed out while you take no more damage.

For better explanations, see: http://us.battle.net/wow/en/forum/topic/969727226