I'm a pet person who never has enough space for pets, so I always choose the pet slot totem. I've exhausted all other means of getting pet slots, so this is the only way I can get more.
I currently have 3 locked in my inventory, because I haven't really found a use yet. I guess I'm waiting till I can use them for pet slots, but honestly I don't think I'll ever need that many...maybe I'll use the next one for a GA medal as having 4 locked boxes just seems like way too many :(