The desired setup for most riding is to have the saddle at such a height that your legs are almost straight, only a tiny bit of bend in the knee, when the pedals are at the bottom of their stroke. If you think about the basic geometry of a bicycle, and the fact that you need some clearance between the ground and the pedals, this correct setup will result in not being able to put your feet flat on the ground when on the saddle. In most instances riders can either barely touch with their toes or cannot touch at all when in the saddle, and so nee to move forward and stand over the frame in order to get feet planted on the ground when stopped.
Another option is to stop next to a curb or other road feature that is raised up a couple of inches and put your foot on that, but this could result in forgetting to step off the saddle when no feature is available and falling.