- Roleplay (renaming your pet)
- Reminders (naming a monster you know is permanently blind, etc.)
- Allows you to differentiate same-race monsters in a group (to find out which one is carrying the wand of fire, etc.)
- Allows you to abuse the Astral call bug (though this is fixed in most variants and on nethack.alt.org)
- When trying to tame a magic-resistant monster like a master mind flayer, you might get large quantities of pets - name these so you don't accidentally sacrifice one.
- Leave a funny death message (killed by a soldier ant called Go Team Ants)
- Let the MSGTYPE option filter away pet battle messages.