[Neven Mrgan just blew my mind][link]:
>Layer comps is a panel—found in the Window menu—which helps you organize different versions of a designs or different views of it in the same file. If you are a responsible digital citizen at all, you probably have some sort of system for keeping around alternate elements and various “views” of your app. Layer Comps will make this easier and more robust.
Had no idea this even existed.
[link]: http://mrgan.tumblr.com/post/134283303/layer-comps “Layer Comps in Photoshop – Neven Mrgan's tumbl”