@guix I use it for two reasons:

1. To try out software, without worrying about cleaning up afterwards. Yesterday I was looking for a Makefile linter, #guix shell enabled me to quickly try out both checkmake and mbake.

2. To automatically setup an environment with direnv and a manifest.scm file. For my plain text accounting I need bc, gnumeric, hledger, miller and xlsx2csv. I do not need these packages anywhere else, but when I step into my accounting directory, guix shell makes them available.