I was taught (many years ago, shortly after they removed the need for someone walking in front of you waving a red hankie) that if stopped in traffic you should always have the handbrake applied in case you were rear-ended by some dopey twat. If you didn't have your brakes or you'd be likely knocked forward much harder into the car in front. If everyone didn't have any brakes applied then the domino effect would continue quite far up the line of cars.
Riding the brake pedal was considered bad as it wasn't as strong as the handbrake and when being smashed into from behind the brake pressure would be reduced (as the car lurches forward before your foot catches up with it).
Modern cars that auto apply brakes when stationary would obviate this a bit.
- Checks license: 1993. Gah.