From what I understand it has to do with how the cpu scales from min to max speed. Unfortunately I don't have a deep understanding of how it works. I use smarassv2
I didn't knoe either... excpet that each one scales for different loads... so I downloaded an app called cputuner from the market. It has advanced options that allow you to set the percentage at which the individual governors scale up. It helped me understand how each one scaled up diffeerrntly.