That’s a great way to get one of the benefits of nix. But you still can check that snapshot into version control, share it with all your machines, etc.
You're right ... you cant check that snapshot into version control and share with your machines etc. When you need that level of control and need to scale your configuration to other machines NixOS sounds like the right choice. If it's for your own machine and you just want to try out a new windows manager non-destructively use snapshots.