answer:I find it confusing, too. A while ago I looked for an answer but I still don’t know. 1) This link says “With back up & sync turned on, you can delete local copies from your mobile device but keep cloud copies saved in your Google Photos library.” 2) HOWEVER, on that page, I clicked on Backup & Sync – How does sync work and it says, “Changes you make to your photos, like editing and deleting, will happen on every device that syncs to your Google Photos library.” Google doesn’t give a straight answer, so I keep Google backup & sync turned off. Instead I let Dropbox on my phone and computer copy my phone pictures. After the computer grabs the pics from the phone, they are safe, and I delete them from my phone.