Lights off last few days?

I believe it was Sannie on opengrow that was saying many varieties will do better on a 11/13 instead of 12/12, and I also read somewhere that certain varieties need more than 12 of darkness, and some need less. Does anyone experiment with these times? Also, many places tell u to turn the lights down to like 10/14, then 8/16, then off for the last few days before harvest. Even Barneys farm i think said to do that for one or more of their strains. Please post your experiences. Why dont i see more growers doing this?