When you turn on the option to show Google Photos in Google Drive a folder is created in "My Drive" where all your photos and videos appear in folders by year and month.
In Drive you can then organize and edit files at will, without impacting Google Photos , and with risk of deleting or breaking existing Google+ posts.
But if you delete a photo from My Drive, it is deleted from Google Photos, and thus potentially from Google+ posts.
I have just this morning discovered to my horror that:
1) It appears that photos copied to My Drive by this feature do count against your storage quota even if they are under the free and unlimited size level in Google Photos.
2) There is no way to remove these photos from My Drive. They stay there even if you turn off the feature, and can not be deleted without breaking Google Photos, Blogger posts, websites and other places you have used the images. Turning off the feature only causes no new photos to be added.
I turned on that feature awhile back when it appeared. It didn't think much of it. But Now my Drive is at quota. I turned the feature off, but soon I will either have to pay +Google for more Drive storage that I do not want to use, storage for files in Drive that Google created, files that are free in Photos, or I will have no option but to stop doing what I do on Google+ and elsewhere using Google services. My Drive will be frozen at its current state.
If you have the option turned on, I would strongly encourage you to turn it off now, before Google gets you painted into this corner. On mobile, it is a Drive option in Settings, right at the top.