Used to use a computer when I rode road. Never on the MTB. I'm quite certain I'd crash if I was looking at the darn thing too much. Since going rigid ss I've taken all stuff off my bars that make it feel cluttered and/or loosens up when bouncing down the trail. Started out being pretty religious about MapMyRide on my phone when on the trail, but more and more I forget to even launch the app and I just ride. I do turn off the ringer too. Started out keeping it in my Camelbak, but now I keep it in my pocket in case I crash and can't get my pack off, etc.