Your friend's practice seems a bit excessive to me, though I can understand one adopting some good driving habits to reduce wear and increase mileage. It usually leads to more safe roads too, due to less aggressive driving behaviour.

A thing I can't understand are screen protectors used by people with an office job. The amount of R&D put into modern phones' screens and oleophobic coating is huge. Your phone's screen is designed to withstand both hits and dirt, to let your fingers slide with minimal friction and to allow you perceive every last pixel of your QHD panel (which has its own huge amount of R&D). Why would you miss all these by gluing a $5 piece of plastic on top of it?