Hi. I have been trying to figure this out for a long time. I even posted in the google support forums and got a bunch of bogus answers.
There is a sync option for google photos under settings>accounts>google. There is also a backup and sync option in the photos app itself. My understanding is that backup and sync in the photos app will sync my photos to the cloud, and any changes made will synchronize between my phone and the cloud. What does the google photo sync option do under account settings?
I have tested this extensively....I used my wife's phone to sign into my google account. I turned backup and sync on (in the photos app) on MY phone so a few pics would go to the cloud, and then made sure I shut it off on both phones. The pics appeared on my wifes phone under photos once they were in the cloud, even though I had backup and sync turned off on both phones in the google photos app. I also checked and made sure the sync option under google account sync was off. I then tried deleting a pic on my phone, and sure enough, it deleted it from my wifes phone. I found this odd so turned off ALL sync options, even app data, in my wife's phone and tried deleting another pic on my phone. Sure enough, it deleted on her phone. I also tried turning backup and sync on in the photos app on my phone, and still had ALL sync options off on my wifes phone. Her phone got the pics as soon as they went to the cloud.
Even more interesting: When I turn backup and sync on in the photos app, then go to the sync options under google account, there are TWO options - google photos, and google photos backup!? When backup and sync are on in the photos app, the switch for google photos backup under google account gets turned on, but the google photos switch remains off. This proves that this google photos sync switch is separate than the backup and sync in the photos application. BUT WHAT DOES IT DO and why are photos syncing to my wife's phone, even when I have ALL sync and backup options turned off???
I am so frustrated with google lately and the way they have over-complicated everything. I've rooted plenty of phones and am not a newbie to this stuff so I don't understand how the average person is expected to make sense of this craziness. They offer no support except the google support forum, and I got a bunch of answers there that I could quickly disprove were true.
