That was handy.
It's still small compared to the 15GB bonus Microsoft has been giving away for the past while for using its OneDrive app, i.e. 30GB for syncing or backing up photos.
Like Dropbox, OneDrive also syncs photos and videos to the PC. As far as I can tell, photos and videos backed up by Google+ can only be manually downloaded to the PC from from its web interface. Google Drive does not sync them to the PC.
Another advantage of using OneDrive to backup photos and video is that they don't take up space on your Google Drive account. Even though Google Drive and Google+ don't sync between each other, videos and photos over a certain size on Google+ still eat into your Google Drive storage allowance.
Of course the downside is whether you trust Microsoft to store your photos.