It gets confusing when you use all google services though, because while google photos technically use your drive space, they aren't really exposed that way. Android generally gives you a warning that when you delete a photo that it's also being removed from your cloud storage too though. But google photos will also constantly prompt you to let it delete your local copies and only have the cloud copies, so you end up having no idea what they are actually doing. Just drive itself is pretty straight forward though since it's mostly separate from the phone and deleting from the phone has no bearing on what's on drive, unless you deleting from within the drives app itself.

Come on! Google Photos is not confusing at all. It is very clear on what it does, but I may be biased.

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.