If you hadn't noticed already, any pictures shared with or by your friends during a Google Hangouts chat will automatically sync up with Google+ Photos, organized into albums by conversation. These images are uploaded even if automatic back up is disabled inside the Google+ app. New albums can be found under the "Albums" tab and are titled Hangout: [Your Name] ● [Contact's Name] unless you explicitly gave your hangout a title, so you shouldn't have any trouble finding them.
I imagine this feature will provide peace of mind to people who hold mission-critical conversations via Google Hangouts. As for me, I'm afraid it will just be spammy.