when you are attacking with the ball and running full speed, you want to slow down and slow down your momentum so that you have enough time to react and beat the defender.
if you beat the defender and are 1v1 with the goalie, you want to slow down and lower your momentum but not all the way because momentum makes your shot better.
when kicking a freekick, the anticipated distance matters. you want to kick the ball with enough momentum to kick the ball over the wall and in the top corners of either the left or right side.
when both the defender and attacker are running full speed at each other trying to get a 50/50 ball, they are building up their momentum. one of them has to apply impulse on the ball to get possession of it
when you want to play a long ball, you have to kick the ball with a lot of force which is you applying an impulse. if you applied enough force and impulse on the ball, it will have momentum and the ball will get to the other side
when you get the long ball played to you, you slow the balls momentum down by stopping the ball with your feet