[Tom Goldman]

A simplified explanation is that they are like a vehicle with a governer used to limit speed ,or in this case ET.
Since most cars running Super classes are capable of running anywhere from 1 to 2 seconds faster than the class index ,running the car at a predetermined RPM controlled by a timer ,set by the racer is a "simple" way to acomplish slowing the car to the desired ET .
By doing this early in the run ,greater trap speeds are realized,while running a disproportantly slower ET.
Horsepower is a lot cheaper to come by now than when the classes and their ET's were established ,so racers have to slow the cars way more now than years ago ,when many had to struggle to run the ET for the class.
There is a great deal of math and science involved in running these cars, some people love them ,others hate or simply dont understand them.