Another way Google Photos is transparent is the app will actually let you know that many of the photos on your phone have been backed up to Photos. The app will

Another way Google Photos is transparent is the app will actually let you know that many of the photos on your phone have been backed up to Photos. The app will ask if you would like those backed up photos to be removed from your phone. (And it'll ask you every time since it doesn't assume that if you said "yes" once then you mean "yes" every time.) So, there's no question about where your photos went when you can't find them.