This isn't a new practice for CO at SFO but we have found that it works to speed up the boarding process. Most of the people that bring their bags to the gate are doing so to avoid the checked bag fee and are delighted to give up their bag at the gate before boarding. This incentive is aimed for the infrequent flier that always is clogging the boarding area and must get on the plane asap. Also if we get these bags early enough the rampers can load them and close up the cargo bins sooner.