For me it's a huge battle because I'm very OCD about my Apple products. VERY! I'm currently going with my 2016 15" 'naked' and hope that I can keep it in as good a shape as possible. I also run my iPhone 6+ and iPad Pro without a case.
To answer your question, it really depends on what kind of person you are. If you're like me and have OCD tendencies, you might be OK. Without much effort, you can easily mark up the anodized surface. With that said though, I've seen these things take incredible falls and continue chugging without issues. And yes, they do easily dent, it is aluminum after all. I have little mental ticks I go through when packing the unit into my carry bag. Those ticks and tricks have become SOP. Also I'm very careful about carrying it around or sliding it on a surface. After a while, I don't even put thought to babying it...just becomes second nature. That said, accidents do happen, you just have to be prepared for it and willing to fix it if it does.
I had a case on my old 17" for many years...the case somehow managed to put it's own marks and wear into the device. I personally can't stand them. Reason? I enjoy the natural aesthetic of the device too much. Apple put a lot of effort into the industrial design of it. Guess I really appreciate that part of it. Plus, I personally hate the extra weight (even if minor) that cases add. Like I said, I'm picky.
I've got a 2014 15" at work that I've babied around. It's in phenomenal shape with a couple of very minor blemishes on the bottom of the case. No one but me would probably notice them. I guess that's pretty good for 3 years.
In 2005 I slipped on ice and my elbow landed on top of my laptop bag. Destroyed the screen of my old iBook G4 (the plastic on those old units was impossible to keep in good shape, I swear looking at it wrong would cause the finish to spider)! I was a store Genius at the time so access to parts was simple enough. Swapped the entire assembly without issue. Repairs like that are much more tricky these days...I'd personally be willing to pay extra for AppleCare accidental coverage if they offered it.
Not sure if I helped or not, either way, best of luck with whatever direction you choose!