Answer :
It's important because you have to know when to make it go faster or else you might not be able to go upside down or in a circle
Knowing how fast a roller coaster travels at certain points on a track is usually used to calculate how much kinetic and potential energy the object has at that position. This is because total energy is the sum of kinetic and potential energy. Since kinetic energy is associated with velocity then knowing it as certain points on the track will help you calculate how much kinetic energy the object has.
