If you have a large, full size keyboard that is already taking up a large amount of space on your desk, and you have a large desk surface, then I agree the wireless keyboard doesn't seem like huge benefit.

I've had big and small keyboards. With smaller one, I find myself setting aside to make more room on desk on ad-hoc basis, since my desk is rather small.

Also, having a wire sticking out of small keyboard perceptibly creates more visual clutter. Could just be me ;-)