This is just from personal experience so take what I say with a grain of salt.
Even though I have relaxed hair, my strands are pretty thick. Up until recently, I protective styled 99.9% of the time (buns). I retained a lot of length with buns, but my ends also began to thin out from being constantly damped with water/moisture and then immediately twisted and manipulated into a bun afterwards (granted, I was also stuffing my thick hair into tight buns to "protect" my ends). The weird thing is that my hair always felt better when I wore it out/took it down after a long day, but I would still choose to PS constantly because that's what I learned was best for retaining length. During my last stretch, I bunned for six months straight (few exceptions) and ended up having to trim a lot of length off to even my hair out and recover from split ends. My hair is still a little damaged from all that bunning, but it's in a much better state. Right now I am rocking ponytails, low manipulation styles (braidouts/bantu knot outs), french rolls, and/or LOOSE messy buns and my ends look much better than they would otherwise. For me, letting my hair "breathe" actually improved the health and resilience of my strands.
Also, I always take my hair down at night and just pin my ends up and cover with a scarf. The tension from sleeping in a tight bun/updo doesn't sound healthy to me. I'm also wary of wearing braids/wigs/etc. for a long periods, as I've had many family members who have suffered through thinning and breakage from wearing their hair in these styles for months at a time.