And I can add from my own experience that this policy also applies to any photos you have on Google+.
Thus, if you are creeping toward your storage max, you may want to move your photos and videos from Google Drive and Google+ to Google Photos, where, if you have selected the High quality option (as opposed to Original), your photos and videos do not count against your Google storage quota.
Next, click on the little blue exclamation point next to Google Drive and you will be shown a list of the files that count against your quota.
Lastly, you will then need to go back through Google Drive and Google+ and delete the photos you downloaded and then uploaded to Google Photos.
Again, it's easier on Google+ because each album has a Move to trash option, saving you from going photo by photo.