Like any tool, its usefulness depends solely on the user. So expect to get a variety of mixed answers.

Personally, using a tablet is easier to sketch out wire-frames for doing people, that is really the only significant disparity I've noticed between a mouse vs a tablet.

However, again, the tool depends on the user, and in my case it is quite possible to knock out a decent human model via mouse.

As an example, here is an edit i did for someone using only the mouse: