Section 3.2 of the manual gives an example of how a user can source their guix profile script. In the example, the GUIX_PROFILE environment variable it set, but then in the subsequent command, it is unused.
This seems unnecessarily repetitive, and also potentially misleading if it is in fact important that when the etc/profile is sourced, GUIX_PROFILE is set to the directory under which it exists.
I would suggest that the second line would refer to $GUIX_PROFILE instead of $HOME/.guix-profile