I do believe it can do more than that, but it depends on the theme you are using. From what I remember at one point it was only the title bar, but through updates it could do more. Don't quote me though. Also, I found ShellWM had a tendancy to cause problems with some apps. When I would install new applications some would behave badly, crash my system, etc., and it became extremely annoying trying to determine if it was really the application I had just installed, or if it was ShellWM. I eventually gave up. But don't let that discourage you... I install and uninstall applications much more than a lot of people.

If you do stick with it for a while, make sure you exclude any application that does its own skinning. Also, beware of color pickers, ShellWM screwed those for me too.