In my experience, travelling with a wired mouse is a pain in the rear end. Every time you unpack or pack the mouse, you have to sort out the cable and connect it. With a wireless mouse, it's just less hassle and I always prefer a wireless mouse when I'm on the go with my laptop. Batteries last for ages on a good mouse (Logitech M510 in my case, same batteries for months with regular usage) and they're standard AAs so easy enough to get hold of if they do go flat.
There is also the advantage that a cable will drag on a mouse, so you'll have less resistance on a cordless one; possibly more of a win for anyone needing precision (gamers, graphics designers)
Finally, there are enough cables across a desk; being able to remove a couple of them might be seen as worthwhile just for tidiness.
The above said, I still use a wired keyboard & mouse at my home PC :)