“Google+ Photos will of course keep helping you store, edit and share your pics. But if you want to organize all your files, all in one place, Drive is here to help. You’ll start seeing your photos in Drive today—immediately if they’re new, and a few weeks for your entire library—so give it a try, and let us know what you think,” Google states in a blog post. This however doesn’t mean you can get rid of Google+ on your phone just yet. The images will also be uploaded to Google+ and will be transferred to drive if you choose to. The space used will be counted only once.
Google+ Photos has several editing tools, and if you use Google+ to edit images, the edit image will not move to Google Drive by itself. You will have to download it and upload to the drive folder. Deleting images from any place will delete images everywhere. It isn’t likely that you will be able to directly backup to cloud, even if you have Google + app disabled on your device, but we will have to wait to be certain. Google hasn’t specified much in the initial blog post. The post does specify that a new Google Photos folder will be added to drive starting today and your entire library will show up in that folder in a few weeks. Google+ and Photos app integration will stay for now. The new changes will be applicable for Android and iOS devices.