Plus, it helps you estimate how much muzzle and downrange energy the bullet will have to impart into its target. Yeah, you can be accurate as all hell at 200 yrds, but is your bullet still going to be able to take out what your shooting, or will you have a long hike to go on waiting for it to die?
Along with the above, you can also use the data obtained from a chronograph to reduce your powder charge for efficiency or recoil purposes, or increase it to get the most performance out of your hard-earned equipment.