Trivial to change midstack applications. With midstack I mean things like cinnamon, gnome-shell or plasma base files. For example what if you wanted to switch from gnome to kde? A single word changed in the nix config file will rip out all of the gnome stack and put the plasma stack in instead. As if you never had gnome on your system, a reinstall for all intents and purposes. Again, trivial to change back.

In case you’re doing this, I suggest you look into specialisations - it’s how I solved that particular issue. It’s not like you’re saving space with your approach anyways, as the files still live in your nice store anyways, otherwise you’d need to download them again every time when switching.