These days, many videographers are one person shops, meaning you are the talent, the camera operator, the director, the producer, the editor and the person who has to clean up at the end of the day.  If you are working under time constraints or if your camera is in a difficult to get to location (say up high on a jib), you can end up with a lot of useless footage of you going back and forth to start and stop filming, or even for adjusting focus.  Canon has elegantly addressed this.  Let's see how.