CPC is called command rate in other BIOSes. All nForce2 chipsets have CPC on by default.
Sometimes you'll see RAM timings listed as 2-3-3-7-1T where 1T is command rate.
CPC on = command rate 1T
CPC off = command rate 2T
If you have problematic memory modules you may need to set CPC off for compatibility. It can also help you reach higher FSB overclocks, but it may not be worth the performance hit, as CPC off is slower than CPC on.