Perception can be used against a target, if it's designed that way (in other words, to block a certain type of Perception).

Perception is frequently an integral part of getting another Demon Ability to 'do what you want'.

Using Warp as an example, you might wish to have a Demon that can change the color of things, in which case the demon would need Perception of a type that would allow it act at a molecular level in such a way as to Warp to produce a different color; similarly, the common 'lockpick Warp' requires Perception that lets it see inside of mechanisms.

To use another example, some kinds of Transport might require a Perception of Destination (such as for Teleports that can get the demon to someplace it can't see).