The series I run in, Camaro/Mustang Challenge, we get dyno certified at the beginning of the season.
Based upon that cert, a minimum weight is assigned.
Occasionally, top finishers have their hood sealed and have to report to a dyno to verify their numbers.
So, if a racer runs extremely close to minimum weight, a 1% variance in the dyno number can mean the difference between a win or a DQ ...