If you are talking about the tube in the maf, i have heard that if you rotate the maf sensor, it is supposed to put the sample tube in a better location to get a better air sample. Did that make any sense? Maybe someone else can get more technical for you.
It's like if you turn the MAF sensor around backwards, the air won't flow directly on the sensor, thus the computer will assume you have less air flowing past than you actually do.