When I use google dns, opendns or even my isp's own dns, the ip I get for example, googlevideo.com resolves to my isp's cache. But with cloudflare it gives my a google ip and I get no cache benefits.
Also, anecdotal evidence, uploading and downloading large files to Google Drive and some other websites is significantly faster when I use google dns or opendns. I'm not sure how that works, but maybe the server's returning an ip my isp can't route to in a fast way? My isp is notorious for having bad routes.