DRAM Enhanced Training

What does it specifically do?
I have a ASRock P55-Pro/USB3, and in the bios under DRAM Timings, there is the option to enable or disable dram enhanced training, but nowhere does it say what it does. Tried googling it but no luck, only recommendations to disable it. Does it help with memory overclocking? meaning does it "train" itself, and change timings accordingly, or is some kind of tweak or performance level? just wondering, because I haven't actually seen a difference either way.

ANY input would be very much appreciated, THANKS in advance!!

I think that it tightens some of the sub-sub-sub timings, I've never really found out either though.

appreciate the way fast reply