Another possible pro (from the site-owner's perspective) is increased user engagement. When you are quietly loading more content all the time, it's easier for the user to continue to say, "I'll just look at one more post."

On the cons side, as others have mentioned, if you navigate away from an infinitely scrolling page, then click the back button, you often don't land in the correct place.

"good for mobile users"

Well, maybe; mobile browsers are often more constrained in terms of RAM. My Android phone only has 256MB, so infinite scrolling tends to cause the browser to bail out.