Please save yourselves some trouble and read the signs.
Two days ago I was flying out of Washington Dulles, which was very busy due to bad weather on the East Coast. Since I had done a same-day standby from a connecting flight to a non stop, I had to go to 'extra baggage screening'. (That is the norm when you change routing day of flight)
At Dulles, there are three areas on the back side of the electronic check in terminals: Human Check In (ie for those who can't use the electronic check in due to international flights, paper tickets, etc); Ticket Purchase; and Baggage Screening.
The Baggage Screening line is usually pretty short, but that day it was very long. It soon became apparent to me that there were several people in line who should be at 'ticket purchase.' In fact, a fight broke out between a customer in 'ticket purchase' and someone in 'baggage screening' who was really waiting for 'ticket purchase', and tried to cut in line.
I sent several people over to the correct lines - there were even people waiting to check in in the baggage screening line. (I have often joked with United staff that should give me a nametag since I spend a lot of time redirecting people and expediting lines in DC and Chicago!)
When I checked my luggage and left, there were 3 police officers escorting another woman away - she too had been in the wrong line, and caused such a scene that the staff called airport police!!!
Also on Friday I was in the Premier electronic check in line, which was very short compared to the regular line. Several people were turned away after waiting, since they did not hold Premier status. They then had to go and wait (again) in the regular line.
While on the shuttle to the gate, there was a woman who had boarded without reading where the shuttle was going - we were all going to C gates and she was going somewhere else. By the time she took the shuttle back to the main terminal and boarded the correct shuttle, she may have missed her flight.
Today I found myself in 'ticket purchase' to deal with a ticket change, and ahead of me were several people just trying to check in.
So, moral of the story - please read the signs and ensure that you are in the correct line to save yourself some time and frustration. These areas are usually very well marked. If you are not sure, ask someone to assist.