As you know, packages are installed in profiles. The default
user profile is ~/.guix-profile (actually it is a symlink to
the real profile) but you can also install packages to non-standard
guix package --profile=…).
Profiles have generations. They appear whenever you perform any profile action (installing/removing packages). These generations are just symlinks to the previous versions of profile, so you can easily roll-back to any previous generation.
As you may guess, Emacs-Guix provides an interface for profiles and their generations, where you can look at the packages from the old generations, switch to any generation, delete generations, etc.
|• Profiles||Interface for profiles.|
|• Generations||Interface for generations.|