adjustment layer effects

Anything that makes a change to the pixels on a layer. An adjustment layer is just a way of adding effects to all of the layers below it. When you add an adjustment layer you are essentially turning all of the layers below the adjustment layer into a movie. It's is the same as pre-composing all of those layers and then adding an effect to the pre-comp.

The only effects that should not be applied to an adjustment layer are those effects that just need a layer to work on like particle generators. If you normally apply an effect to a solid and it does not make any difference what color the layer is then that effect is not a good candidate for an adjustment layer because it will take over everything and you will no longer see anything from the layers below.