Gate Changes
One thing that frustrates a lot of passengers is multiple gate changes before you get on the aircraft.
Just when you get to the gate you saw on the information screen, there's an annoucement telling you your gate is now at the other end of the terminal, and when you get there it's changed again - what's going on?
Flying is a dynamic environment, and to best understand think in terms of the operational logistics of parking aeroplanes.
If there's a delay on a departure, that gate is now occupied longer than expected and the aircraft that was to park on that gate next has an option when it arrives - wait indefinitely for the gate, with passengers keen to get off the aeroplane, or go to another gate that's open.
Picking another gate keeps things moving, and the aeroplane doesn't have to sit away from the gate causing additional delays.
Operations staff are continously planning ahead to ensure aircraft have a gate planned for arrival time, and each time a change occurs (as described above) another gate is found, but still subject to change.
Without flexibility delays would be more common, as one delay would affect other aeroplanes due to use that gate.
A lot of passengers have felt the frustration of landing and having to wait for a gate to deplane, and departing passengers want to leave on time....
Gate changes are a practical way to use all available resources and with some understanding passengers can realize it's not bad planning, but actually a well managed team effort to make a dynamic environment work.