If you are the only person in a bathroom with three urinals, there is absolutely no excuse to use the middle urinal. The doctrine of the buffer urinal suggests that you should never use the middle urinal, even if there are others using the urinals at either end. But if you are the only person in there, there is no good reason to force a violation of this unwritten rule.

Maxim had a great graphic a few years back illustrating this; I'll see if I can find it and post it here. (I'll also have to print and post in the bathroom, I guess).

Please, respect the Buffer Urinal Doctrine.