Personally I'd never put bedliner on the outside of a body. I don't see any pros to that and a whole lot of cons that have already been mentioned.
I do have a DIY bedliner (Durabak I think was the brand) on the inside of my Bronco. I like it and would do it again, but it's not for everyone.
For me the biggest plus is that it does have some teeth. True, you don't want to slide your knees across it. But the nice thing is that stuff doesn't slide around much.
Another plus is that it doesn't hold water like carpet. I only have a soft top and whether it's on or off, it doesn't really keep water out. Plus I 'wheel it, and I don't feel bad about getting in with dirty boots.
It also stays in place rather than blow around like mats do when driving with the top off.
There are a lot of cons, most of them already mentioned. But none of them matter that much to me. It not insulating against sound or heat is the biggest drawback. But since I wasn't going to have carpet I didn't really have many better options. I don't plan on selling so I'm not worried about resale. Yes it's impossible to get actually clean, but that doesn't bother me.
I put it on pretty thin so it doesn't add that much weight, but the flip side of that is it's not as tough as it would need to be in the bed of a pickup. But it's not in the bed of a pickup, so that's a fair trade.
I never noticed any issue with outgassing, but the Bronco sat for quite a while after I lined it before I could drive it, so it might have just happened then. Also I have pretty good ventilation %) which helps reduce any odors.