I usually fly out of BWI these days, and Delta there has a line to the kiosks followed by the one to drop the bag. If you printed your boarding pass at home and checked the bag online you can Skip the kiosk, or sometimes even drop them at the curb.
In Atlanta, They usually have completely seperate bag drops for those who have checked them online. Again, you can also drop them at the curb.
It really depends upon the airport, and also how large the airline's presence is there. Some airports are limited in the amount of space they have available, or don't have enough traffic for your airline to warrant having seperate lines.
(For Delta, if you checked the bag online, you usually just need to go to the counter and show your boarding pass where they will do the tag and weigh-in. )