nothing imo, it’s main benefit is making reproducible environments, imagine you need 10 machines to have the exact same things running on it, setting up each one would be a PITA and keeping them the same is near impossible, nixos solves that problem.
it’s not gonna do anything for you, most people just want a working OS system on your PC so that you can do the things you need to do, if you have that, there is no reason to be fucking around with nixos.