Reclaim iCloud storage by deleting iCloud backups for devices that you no longer possess
Recently I checked my iCloud storage and found I'd used 31 GB of my 50 GB plan. Most of it — 17 GB — was backups.
When I dug into the backup list, I found one for an iPad I no longer own. Nearly 6 GB, just sitting there. Deleted it, got the space back immediately. Worth checking your own backup list if you haven't lately. Old devices have a way of quietly hanging around.