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:
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