When I was in drivers ed, turn signals were absolutely drilled into us. I've been laughed at by friends and family before because we were on some neglected side road or parking lot and I've used a turn signal. It's just automatic.
Plus, you never know where a cop could be waiting to see someone fail to use one. At Sugarbush 2 of my cousins were pulled over last year late at night for failing to use a turn signal at the end of German Flats Road when turning right onto the Access Road to get back to their condos/hotel after dinner at Common Man. People making a right at that spot often fail to use a signal especially when they think no one is around.