Using Layer Comps in Photoshop CS3
If you use photoshop to create any designs for interfaces, web or print you probably are either using groups to separate pages or separate photoshop documents, or possible Smart Layers. Using groups or smart layers that are intelligently named is a very good way to separate out different instances or pages within a single design without having multiple files. Taking this a step further, as of the Adobe Creative Suite, Photoshop has introduced Layer Comps.
Haven't heard of it?
-- Not surprised, it's sort of hidden and took me a while of digging through this program and upgrading to CS3 before I really started using this feature.
Using Layer Comps
Layer comps 'remembers' the location of your hidden/visible layers, as well as position and layer style if required. In the layer comps panel (Window -> Layer Comps) you can create a new layer comp, or switch through comps similar to how you hide/view layers in the layers panel.
Keeping Layer Comps Updated
Since layer comps remember the location, position, and/or styles of layers, if you remove a layer a warning will popup if you attempt to view the comp that was saved with that layer. You can ignore or update the layer comp, duplicate, and change layer comp options all in the layer comp panel.
Website Design
I found this feature extremely helpful for handing off or receiving website design comps. To accurately view each page of a site design it is best to give separate files to ensure whoever is receiving it is viewing the appropriate series of layers, rather than relying on viewing and hiding the correct layers, or using smart layers within a single PSD, but basically doing the same thing.
With layer comps, I can add comments to the Layer Comp name, and be much more confident in sending out or getting a file from a designer and know that they or I am seeing what is expected, without the hassle of multiple files or the possible duplication of content in smart layers.