It defines how much the calculated steering force in LFS must change before a new FF command is sent to the wheel. The value is used as a divisor, so the higher the value (max 256) the smaller the needed force change and the "finer" the FF nuances. Scawen put this in, because AFAIK in testing the wheel drivers couldn't handle the constant updates of minimal force changes. This setting makes the updates less frequent, reducing the stress for the wheel drivers/software/whatever.
So in conclusion, higher value = theoretically more detailed FF, but higher data transfer. Lower value = less detailed FF, but not so much stress for the wheel.