The idea of impermanence is that upon reboot, the machine loses its state and in the case of NixOS gets recreated from your configuration (stored in a persistent area of your file system). So any erroneous state changes (accidental or otherwise) are lost between reboots.
The persistent area will hold some important data - perhaps ssh keys (depending on type) and passwords that you may need beyond your configuration.nix (or flake)
It does not affect your home folders.
I found Guekka’s blog are good resource - NixOS as a server, part 1: Impermanence | Guekka's blog
I use it - as much to find out more about it as anything else.
If it interests you, try on a spare machine first.
4 Likes