This thread already exists, but nothing anyone really says matters. It's up to you whether or not you want to use a case. I didn't use a case with my s3 and s4. Both phones looked pretty much like new by the time I was done with them.
Then a week before I got my Note 4 I dropped my S4 on accident. It fell in such a way that a hairline crack formed straight across the middle of the screen. The phone is still usable, and the crack is barely noticeable, but as you can imagine, that scared me into wanting a case for my Note 4.
You'll be fine without a case until you aren't; then you'll regret it. Will knowing how many people aren't using a case change your mind one way or the other? Just food for thought.
For the record, I'm not currently using a case since I have the Verizon variant of the Note 4 that is incompatible with all of the cases that I think would be adequately protective against drops.