Functionality of FW_LND_HHDIST

I’ve been tinkering with auto-land and flare parameters for fixed-wing. Can anyone tell me, what exactly the parameter fw_lnd_hhdist does? My understanding is: that when enabled, it tends to hold heading when the plane is a certain distance away from the landing point. Also, can I expect my plane to not veer off to right or left during landing with this parameter disabled?