“They don't 'belong' to anyone - they are anonymous. So the downsides are:
-you can't manage them (add images, delete, etc.)
-you can't extend their expiration
Note though that galleries expire only after 3 month since last use. So if they're used (clicks on images) regularly you can safely use them.
Anyway if you want to have them with your account, send us their IDs (or links) to email@example.com”