I use them in an esp32 to write a random password to each of my products, so when I sell them they can each have their own secure default wifi password while all using the same firmware.
This is the only way I could come up with that would allow an end user to do a full factory reset, and end up back in a known good secure state afterwards.
Storing it in the firmware would mean every user has the same key. Storing it in eeprom means a factory reset will clear it. This allows me to ship hardware with the default key on a sticker on the side, and let's a non technical user reset it back to that if they need to.