Learning one program is easier than learning two. However, there are some things that CC3/CD does that are much easier than accomplishing the same feat in Photoshop. For someone experienced in both programs, the two combined would be quicker and easier. For someone starting to learn, I'd recommend choosing one or the other.

If I were setting out to make something like the Fallcrest map (for instance), I'd start with a layout generated with CD Pro, then take it into Photoshop and do a paint-over. The end result wouldn't look nearly that good, but I'm not (yet) a professional artist, like Mr. Schley.