I was issued a new M&P40 (Night Sights, Mag Safety, no IL FWIW) about four months ago. Other than transition training and qualification, about 600 rounds, I've never fired it. What!?!?!?! you say.
Well, it is pretty simple. I own my own M&P40 also, and when I feel the need to shoot one, I shoot mine. However, I'd be willing to bet that most of my coworkers have also not shot their issued M&P40 any more than I have and do not own one of their own. Law enforcement officers who are not "into guns" are not any different than anyone else, they don't shoot except when they have to.
I've shot my issued M&P enough to know it is totally reliable with our duty ammo (all the shooting we did was with duty ammo). I don't see any reason to subject it to shooting wear. It is the pistol I am most likely to be carrying if I ever get into a shooting, and I don't want some small part to be on the verge of breaking due to the wear of many thousands of rounds if that time ever comes. So, when I want to shoot an M&P, I shoot mine.
I shoot IDPA with my M&P9, so mostly I shoot that instead of my .40 anyway. Recoil is less, but not too much different, and handling and feel are exactly the same. The only real difference is that none of my full-size M&Ps have the mag safety and my duty weapon does.
So far they have all held up well.