There are fair uses for it. If you can't spend much mobile data but Google doesn't waste it or the site went down for whatever reason (you could still use archive.org) then you are using it for it's intended purpose, which is good, but if you are paranoid in the Web like some people, then I'd recommend staying away from AMP links. In the end, it doesn't really matter, since you are always being tracked in the Internet in some way or another.