There are those on B737NG'S, perhaps also AB's, who profess that if you have an FMC generated VNAV/LNAV approach the FD's will give good enough guidance to touchdown. I used to fly for operators that switched FD's off when visual from an NPA. I then had sim checks by TRE's from different operators who did not, as they believed it was not a Boeing SOP and believed that there was some guidance available. I'd always been taught that the A/P connect limit was 50' below DA unless coupled to a glide path. Therefore this applied to he whole AFDS, including FD's. That is not to say the FD's suddenly become inaccurate, but would be advisory only, in some operator's eyes.