You barely talk to the the border agents on the regular line though. What are they really doing to check you? Its the same simple questions, where are you going

You barely talk to the the border agents on the regular line though. What are they really doing to check you? Its the same simple questions, where are you going, wheres home, anything to declare then you go through. The regular line for citizens is only long because there's a lot of people in it, not because they're doing anything special.