Fade is a powerful ability of the Assassin. Once activated, it raises all resists of the Assassin for the duration. It also reduces curse duration, something only the Cleansing aura could do before the expansion. Fade also provides a hidden physical damage reduction of 1% per skill lvl.
Fade cannot be used at the same time as Burst of Speed, so the Assassin will have to choose which one to use. Of course, one could invest in both skills, but that's a lot of skill points to pour into these two skills. For an effective build the player will most likely wish to focus mainly on one.