Delta starts forcing people with rolling bags to check them planeside when they have a full flight because they run out of overhead space. They do that for free. If you check your bag when you check in for your flight, you pay $30 to do it. If you can, take your rolling suitcase with you to the plane and get it checked for free there rather than paying $30 to do things the way travelers are encouraged to do. The airlines are penalizing people who do things the "right" way.