Not all trips are to and from locations on specific timetables, such as work. Sometimes you want to go from your house downtown, or some other location. There's still an average wait of half the train interval time. You can wait at the train station, or wait at home and travel closer to the arrival time (and hope you don't miss it), but there's still a wait involved. Sometimes you can effectively use this time, sometimes you can't. Acting like it doesn't exist isn't useful though.