Well if the accuracy is 95% why not turn all Facebook users into one huge mechanical turk batch process to get to 99.9%? And it's just convenient for people not to have to tag.

Then you have the data sitting around for mapping the insides of all buildings like Google has it for street view. Sure your Asimo-style robot butler/"something really BIG" will be that more efficient with internal mappings of most public spaces when you release it in 2030, but the convenience is sufficient. Remember that Facebook beat Myspace more or less on interface (combined with a few other factors like exclusivity), they aren't going to let Google or some other competitor get ahead of them by having an interface convenience edge of 5-10% which might cause a Myspace-to-Facebook style exodus. Kings who have committed regicide on their predecessor are all too aware of how they got into power.

Also consider this, use SIFT on video stills and collect all the handheld video of a particular concert. Use machine learning to combine all the audio tracks and clean them up into high quality audio. Stitch the video together, using textures from the higher resolution stills people take, to allow people to relive the concert with a massive panoramic video (or 3D) with high quality sound. Use it to launch a music competitor to Google or destroy Ticketmaster (well overdue..) as bands and venues won't have to hire video production companies to record concerts if they sell tickets through FB. All that technology is in current research papers and prototypes at the moment, it would probably only take two years to put it together at worst if they aren't working on it already.

Or it could just a be a way to get users to add more meta data to their data, which allows them to increase engagement