Well, this is actual “in vivo” proven studies 
It’s not just from my own experience, but vast data available. The glass on the screens is tightly closed and hits on the side (frame) can cause it to crack. That’s where the cushion becomes necessity. Of course direct exposure will make it crack and that’s why all of the cases have raised “lips” around the bezels.
The best protective cases available , which are not as bulky as “Otter box” are made by Tech21. They are thoroughly tested by their engineers as well as many reviewers online. They claim that they will keep the whole phone intact if dropped up to 8ft high on any surface. I can attest to that as well my last 3 phones had these cases on and dropped them multiple times from 6 + ft I never had a problem.
The reason for their success is that they added extra layer of rubber and air around the bezels (tiwce as thick vs competitors), raised the lips 50-100% and added a web like pattern on the back which.
In my case, I had less rugged cases and still had my phones survive drops w no cracks or scratches. Spigen is one of the best for slim style TPU protection. They still have added extra support on the sides , but very light in comparison to Tech21. And bunch of no name brands do decent job , but wear out faster (become more lose) than these big names. Though, that’s more noticeable in when it’s taken off frequently.
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