Layer comps allow you to create, manage and preview a variety of images from the same Photoshop file by experimenting with different layer comps (short for compositions). This can save you a ton of time if you need to create a multitude of images that are basically the same but need different text and graphics on each image. A file with a layer comp is smaller than if you had to create each comp separately in a different file. You also have the added advantage of having all of the layer comps in one file for convenience as well as the ability to use them with other applications like Illustrator and InDesign.
It is best to create images and layers in advance of using the layer comps technique and that they be of the same size. Layer Comps will not track any changes to pixel information.
After you create a series of layer comps, you can output them using a variety of formats.
After creating layer comps in Photoshop, you can place the Photoshop file (psd) into Illustrator or Indesign. In both cases, you can choose the option Use Photoshop's Layer Visibility to view layer comp in Illustrator or InDesign.