I think for me crank length, saddle position and cleat position would stay the same for all three.
Don’t be too sure. I went in thinking all I needed was possibly a 10mm longer stem. It went shorter though crank stayed the same. Cleats and saddle position changed too.
From my experience with it, it started with an in depth chat about injuries, type of riding and goals and then exercises to see how flexible you are. Because I competed, my fit was all about getting the best position for power and efficiency. From my original position I was getting a lot of vertical movement form my hips and flat spots at the bottom of my pedal stroke thus not maximising my output. I also had a low back angle of 37° which was restricting my breathing. By increasing saddle height, shortening stem and raising it slightly, it increased my back angle to 40° on the hoods. By doing this I have found instant results in speed and consistent power, especially when climbing.
Once done you come way with a date sheet showing all the geometric dimensions you need to adjust other bikes. The key dimensions for me being stack and reach. From there I can set up my bikes accordingly. Not sure if they transfer to mountain bikes (can’t see any reason why not though) but they can be used for a TT position because when down of the rests my back angle decreases by approximately 10° putting me in a good aero position. I also set up my cx bike with this set up to.
Money well spent in my opinion. It cost me £135 for the fit as he know’s the club I ride for so I got 10% discount. 😀