If you read @Steve's mirrorless AF book he talks about the potential problem and situation where someone 'might' have to use AFFT on a MILC. It has to do with the way focus is achieved, basically focus is calculated and a focus offset value is sent to the AF controller which adjusts as much as directed. If that focusing offset value isn't quite right the lens will miss focus and it's not really a classical control loop where it will iterate and converge towards a solution to get it right. If the AF system tried again the body would just calculate a new value assuming the lens offset to proper focus is correct and still get it wrong. If you ever got a lens that demonstrated that problem, fine tuning could help.Hi @Steve , by that do you mean mirrorless cameras can also have AF tolerance errors like the DSLRs where the camera/ lens combo may have front or back focusing issues or do you mean the AFFT options are available on the mirrorless because some photographers may be deliberately dialing in AFFT values trying to have some front or back focusing? For instance when photographing wildlife some photographers prefer focusing somewhere midway between the critter's eyes and nose/mouth to get both the eyes and nose sharp because focusing just on the eyes may make the nose soft.
IOW, having the AF sensors right on the main sensor eliminate AF Fine Tuning in almost all situations but the way focusing is achieved and those offset values used to achieve focus make it possible that some lens could need fine tuning to adjust those values.