One thing about sitting down for too long, too much blood collects in the legs, and the brain loses out. Standing can keep people thinking, and it makes everybody want to get to the point as quickly as possible. If a meeting is expected to run for a certain time, people will plan their thinking around it. Standing encourages the use of the time as productively as possible, and people will frame their input with that in mind. Shutting the door at meeting time is something people will remember quickly, especially if they know the meeting will be quick, and they might miss something they need to know..