For a long while photos stored on Google Drive were viewable within Google+ Photos, but today marks the first time you can view your Google+ Photos using Drive. That sounds a little confusing, so to put it simply, wherever you've stored your photos (be it Drive or G+ Photos), you'll be able to view them using whatever service is more convenient.
This is good because if you're like me, you'll have gigabytes upon gigabytes of photos from your childhood on Drive, dating all the way up to 2011, and the rest being backed up to Google+ Photos. Now I can look at my photos all in one place, which relieves my OCD a little...
In Google's announcement, it is stated that new photos will be viewable in Drive today, but may take a few weeks before your entire photo library is viewable. A new "Google Photos" button will appear on the mobile apps and on the web when it is rolled out to you.
It is important to note that even though your photos are viewable in both services, they only count towards your storage limit once. Also, if you delete a photo from Google+, it will be deleted in Drive and vice versa.
You can learn more about today's update by checking out the Help Centre article here.
Source and image: Google Drive Blog