Many projects do both ways, the “local” flake on the repo serves as a source of bleeding edge package and “blessed dev env” (specially useful when combined with direnv, because you just git clone, direnv allow and then get to business) while nixpkgs hosts the lastest release/stable version.

It welcomes testers without alienating everyone else.

the trigger for me to switch was when I tried to include the mempool app to nixpkgs. I got hammered cause bitcoin apps were supposedly bad for the environment at that time.

from that moment on, I figured a little decentralization was my way forward.