Hi there! When a pet is on your profile it continues to age and requires feeding so that it doesn’t die.
In contrast, in your showroom/gallery the pet’s growth is essentially frozen - it won’t age at all and it won’t grow hungry so you don’t need to feed it.
So, your showroom is a great place to store your pets if you aren’t worried about ageing them, as you won’t have to keep buying food.
I hope that helps! Let me know if you have any more questions :)
Edit: Hehe Koopa beat me to it