In PvE, this skill works well to disable monster's elites since you know what skill they will bring; additionally, since many monsters don't have a full skill bar, this will often disable a key skill. In PvP, most elites play a key part in people's builds, and disabling them will often cripple them.
Anomaly! If the target has more than one elite skill in their bar, for example from Arcane Mimicry or from a capture, this signet will disable multiple elites. Some PvE foes also use multiple elite skills, making this skill effectively shutdown two skills at once.
Anomaly! When used on an invalid target, the message displayed is "Invalid spell target.", even though this is a signet, not a spell.