@mcg I didn't intend to post that without finish writing the answer!
I've tried many times to use Photos to manage a part of my photos, but very soon I've given up in despair since I have huge difficulties in separating finished photos from others.
I think that Photos tries to do too many things: being an archive of photos, a scratchpad where to store current work, a place to store temporary photos (like from where the car was parked, a phone number, etc), a place where to exchange image info between apps, etc.
In my mind everything gets too cluttered. But this is just me.