Bookworm. Not quite sure what you mean by the FSD but assume it is the localiser and glide slope info on the ADI and HSI?
Normal LOC deviation is one degree per dot. When VOR/LOC engaged (not necessarily on auto pilot either) the ADI scale automatically expands to indicate half a degree deviation per dot. It remains expanded until after landing roll-out or on a go-around with RA greater than 200ft.
There is no distance lateral deviation indication on either the expanded ADI scale or HSI although you could work it out by mental arithmatic if you knew the exact distance from the localiser aerials. Forget that for a joke. But as an example if you are 5.486 miles from the threshold then one dot on the normal scale on the HSI means you are 774 feet off centre line.
If you fly the ILS without the flight director then the ADI localiser scale is the same as the HSI - that is no expansion. In that case if you are on MAP mode for situational awareness it doesn't really matter because the ADI localiser gives you all the information necessary to tell you exactly how many dots you are off the centre line.
Put another way - if you allow the aircraft to stray off the centreline full scale on normal HSI mode then it is an immediate go-around situation. But if you are on MAP mode and relying on the expanded scale on the ADI to keep you within limits when on flight director, then you are whistling into the wind
Of course a brilliant PNF would quickly advise the PF that he had deviated off scale on the expanded ADI when on flight director coupled to ILS. But the moment that the PF allows the aircraft to drift off beyond full scale on the expanded localiser you are rapidly going into no-man's land especially if you are maintaining the glide slope.
In the simulator we were unpleasantly surprised how quickly the expanded localiser moved to off limits while at the same time we were unable to detect a significant lateral displacement while staring at the MAP mode even on the 10 mile scale.
At no stage did the expanded scale automatically revert to normal scale even though we had reached beyond full scale displacement on the HSI normal scale. I believe a safer design philosophy would be to have automatic reversion from expanded scale on the ADI to normal four dots if a significant lateral deviation occurred.