- Place a photo in a Polaroid border, without having to crop it. Keep its full resolution so you can scale and rotate it as much as you want.
- Texture a chess board. Combine the texture layer with layer effects applied to the base layer.
Addendum: You can use any layer as a clipping mask, not just vector layers. Plain-old bitmap layers work great too, if you need a “paintable” mask, or if you have a transparent PNG you want to use as a mask, for example.