The Motor Accuracy function is used to compensate for Backlash which is inherent in all moving part systems including motors and lenses. Even if the motor was 'perfect' (which no motor is), there will always be backlash in the lens itself and in the flex in the rod/mounting.
Generally it is worse to have this number set TOO HIGH than it is TOO LOW. So we recommend a value of 1-5, unless you see better results on your typical rig/lenses with a slightly higher value.
In almost all scenarios we would recommend just leaving this setting at it's default of '2' without changing it.