If your a reloader and a long distance shooter, then a chronograph becomes "thee" most important tool in your reloading tool box.
Once youve developed your accurate and consistant loads (if your reloading) then you need to know your speed.
Theres other "exact" inputs (ie: altitude/temp/barometric pressure/type of projectile/distance from center line of scope to center line of barrel etc...)needed in ballistic calculators to give you bullet drop at what ever distance,s but without knowing your "exact speed" is like driving blind.
Theres nothing better than to spend countless hrs behind load development trying to achieve 1/4 moa @ 100 yds, then calculating your bullet drops at different distances via ballistic calculators, going out, setting up steels at exact distance,s , even out to 1K and smacking them 1st shoot because of you knowing your bullet speed for ballistic calculations.
Knowing what your bullet drop is at what ever distance is one thing. Figureing your adjustment on your scope weather it be in mil/moa is another. Its not rocket science. Once youve figured it out?......watch out...its one addictive hobby for sure.