I understand what a progressive rate is, I was just uncertain what kind of suspension people with progressive springs were trying to achieve. Having progressive springs doesn't mean that your wheel rate is going to be progressive. If your suspension geometry yields a regressive rate, equally progressive springs would change your wheel rate to a linear rate, which is usually ideal for racing.

BTW, when a spring compresses, each inch stacks on the previous inch. For example, with your progressive springs that vary from 160 to 300 lb/in, the first inch would be 160 lbs, then the next inch would 160 plus the rate for the next inch. So, in order to compress the spring 2 inches it would take, for example, 360 lbs, then 600 lbs at the next inch. The compression you described would be a regressive spring rate.