As creator of small tools, my flakes might often end up in other peoples
projects. Overlays are a performance problem in those use cases because
I would kept re-instantiating nixpkgs instances. Of course I could also
expose my stuff as overlays as well.
In that case I would need to merge downstream dependencies like
go2modnix as well, which would polute their nixpkgs instance with
unrelated stuff and also make it harder for my users to tell what random
attributes came from which place.
