Try enabling Google Photos to automatically upload images from multiple devices to the same account.
If Google Photos is low on space, try deleting from Google Photos without causing it to delete from all other devices. Seems to require manually copying all those files to an untracked folder, then deleting from Google Photos.
Try managing which folders Google Photos syncs:
When it asks to add a newly found folder, the app doesn't give any way to find out where that folder is or what's in it, unless the folder's name only occurs once on the device.
Try removing folders from the app ("Whups, didn't mean to backup all the graphic assets of a random app that foolishly doesn't use 'nomedia'!"), where the folder name is not unique. It again gives nothing more than folder names and no indication of where they are or what's in them.
Try getting Google Photos to list where every file first came from, so you know where the originals are (for various reasons).
I take photos on my phone, and they are automatically backed up. I can access them on all my devices, and I have them even when I change my primary phone, so I am happy. I only backup my camera photos, so I guess my needs are simple. So it suits my needs. I can disable it from backing up any other folders, so random photos don't end up in my library. I never needed to find out where a photo was backed up from, because I only care about my camera photos.
