Crop body = 1.6x extra reach. Talking about the 7D, you also get 8fps. That's just awesome. After buying the 5D Mark III, I was planning on selling my 7D and EF-S lenses, but I decided against it. Other than the first two reasons listed, the main reason I couldn't part with it was my EF-S 17-55. I love that lens so much that I had to keep a body to use it with.
The 17-55 is a great lens, indeed, I used for several years. But ... the 24-105 on FF is even better, and not much different in weight and price.