The interesting interview[1] with Bradley Horowitz (Google's "VP of Streams, Photos, and Sharing") directly addresses that.
Obviously, machine learning will benefit Google. But it will also benefit all the users of this service, by improving the automated assistance of managing your photos (some of which is already pretty neat, like the automatic photo albums Google will sometimes make for you).
If you are not a photographer, and say, you have kids, you definitely don't have time to do that much curation of your photo archive. You might set aside some time time make a share a photo album after a major event like a birthday party or something, but you will never have enough time to manually derive all the enjoyment our of your photos that you could be getting. This problem needs smarter machines to solve it.
Relevant quote:
Q: You use artificial intelligence to surface photos on a given
theme, or find specific people in the photostream. What’s the
percentage of getting it right?
A: It’s good enough. It’s not perfect, in the same way that voice
transcription five years ago was not perfect. The key to getting
that last percentage which tips it over will come now, when we deploy
it at scale. Getting all that data will create a virtuous cycle of
getting better and better.
[1]:
https://medium.com/backchannel/bradley-horowitz-says-that-go...