2) when set on a flat surface, it creates an unstable bridge, meaning downward pressure on the phone is not supported. Think of how a piece of cardboard would react to being pressed down in the middle with only 3 of its corners supported.

3) It creates a point that can be snagged when moving the phone around, either on clothing or surfaces it's set on.

Personal opinion, it's really frustrating to have a phone that doesn't sit flat on a surface, to be unable to easily use it without some kind of case or holding it.