Multi core enhancement basically puts the highest turbo multiplier on all cores under load. Let's say you have a 3770k. The base frequency is 3.5ghz. Under normal circumstances, it will be at 3.9ghz if one or two cores are being stressed, 3.8ghz if 3 cores and being stressed, or 3.7ghz if all 4 are under stress. If you enable multi core enhancement, it automatically puts the turbo multiplier to 39 under any load situation, regardless of how many cores are being utilized.