Submitted via IRC for SoyCow5743
Google will automatically delete all of a user's Android backup files — stored in his Google Drive account — if the user does not use his phone for two weeks.
Source: https://www.bleepingcomputer.com/news/mobile/google-will-auto-delete-android-backups-if-users-dont-use-their-phones-for-2-weeks/ [bleepingcomputer.com]