The terrain and duet handbrake is designed to slow the stroller down as opposed to bring the stroller to an immediate and permanent stop. This feature is useful when tackling declines during everyday use.
While walking down hill, squeezing the handbrake to maintain a constant speed can save on you having to lean back or take a lot of strain, making your life a little easier and safer.
The foot park brake is designed to maintain the stroller in a stationary position.