It depends on your use. Once a month for a range trip? Turn it off.
I carry my RMR 07 almost every day. I want to know it is always on and that I haven't forgotten to turn it back on because of a brain fart. I leave it on, sometimes just adjusting the brightness depending on the environment.
It is also my primary home defense gun, so I want it on at night too. It doesn't make sense for me to be turning it off/on.
Yes, you can wear out anything, including the rubber cover to a switch, if you use it too much.
If I know I will not have the gun on me for a week, say while traveling, I turn it off and leave it in the safe.
I change the battery once a year, even though it has a 2+ year life span.