It's good to have a choice. I know I'm going to drop my phone from time to time, and sometimes it will be onto a hard surface, so I always get a case. I once managed to shatter the back glass while it was in a case, not sure how I managed that. Other people may be less clumsy, or more tolerant of living with damage, or more willing to pay for insurance or replacements.

It's also nice to be able to choose a texture. In my latest iteration, I got Apple's techwoven case, and I really like the feel compared to the usual silicone stuff, or bare metal. The texture also makes it easier to grip so maybe I'll drop it less. I can hope.