REALLY?
Has that happened to you?
Or someone you know?
I have taken the screw out and never had a problem, , , , yet?
Never happened to me.........but.......
I remember some pictures on the Zumo forum aboput a year ago (
d00D would know most likely) that showed a Zumo that had fallen off a moving bike. It was a mess.
The screw locks the top lid down. Without the screw in place, if you hit a big bump while riding, it could knock it off. Another possible problem is while reaching around the Zumo a hand (especially with gloves) could accidentally bump the top lid up & then the Zumo would fall out of it's mount. Either situation is not a good one. The screw prevents both.
My 1 1/2 cents (deflation).