I'm pretty sure every Dot on any DPS is a must. I really don't agree that every DPS should be, but that's how it is

Mutilate is a power of 60 with a DoT of 30 for 30 seconds.
Dots tick every 3 seconds, making it 10 ticks.
Over all the dmg of the skill is 360 for only one GCD, modified by both Dancing edge and poisons. (not to mention trick attack)

That said, it's one of your most powerful weapon skills.