Also note that it’s far from limited to snark against a fellow poster. I assume a single rolleyes reply to a post in GD with nothing else would warrant at least a mod note (as would a snark that Measure for Measure would choose to write out). But other than that, they do get used (as do words) in intra-dope conversation all the time.
But they’re used a lot more than that. Here’s a random use from a recent thread:
Not the same communicative value. Unless he really did lick Wikipedia’s pie.