One thing I've noticed more and more on flights is that we generally leave late
But then, the pilot always comes on and says something like "sorry about the delays folks....blah blah blah...but it looks as though we can make up some time and that'll put us in "destination x" on time"
Then, as sure as were were going to leave late, we land and arrive at the terminal only to wait for 20 minutes to get an avaiable gate.
I don't know whether or not it costs more fuel to make up time (I'm assuming the flights are designed to run at optimal cruising speeds for fuel economy) but it makes no sense to burn up extra fuel, just to arrive early and sit and wait for a gate. That happens on AT LEAST 2 out of every 3 flights I take.