They send random gifts some times, usually a code to redeem something in a game I don't play.
Some super reacts - animated emojis basically.
Other than that I really couldn't tell you. I don't think the subscription is worth what the subscription gives, but the alternative is the free product gets worse faster, and that would disrupt a lot of communities that I enjoy interacting with.
Thinking of Discord as a whole, I think it is worth the nitro price. Not in love with the trajectory though.
Most OLEDs today ship with logo detection and will dampen the brightness on static elements automatically.
While it isn't a silver bullet, it does help reduce burn in since it is strongly linked to heat, and therefore to the pixel brightness. New blue PHOLEDs are expected to also cut burn in risk. Remember that LCDs also used to have burn in issues, as did CRTs.