Value to whom? The site loads faster (so people like it slightly better), it's easier to maintain (less files to serve and keep track of), all for the cost of something the site owners didn't pay for in the first place.
This is often repeated but without any data to back it up its a bit of a myth.
My tests show local resources consistently loading faster than making a link to Google. These are supposed to be cached but thing like fonts are always loaded again. Anyone can repeat this for themselves.
Edit: here's the ToS: https://developers.google.com/speed/libraries/terms If you believe Google, they're not collecting anything.