Hmmm, let me think... does it help to not have my arm dangling in the air for hours at a time? Uh, let me get back to you on that...
When I set up my first PC, back in 1992, the first thing I did was pull out the filing cabinet drawer on my right, put a couple books on the top with a mousepad on that. All for the very same reason. Makes no sense to have to reach up to the desktop to use the mouse all the time.
A few years ago, I had rotator cuff surgury. The first day out of the hospital,
I built this. I didn't own a digital camera then. Those were still captures from my camcorder. Here's a
picture of it, just before I gave it away.