Let me just add a bit more:

I can see that if the mass the stepper motor has to move is too great for an "instant" start or stop, the only way to avoid stepper missteps is to ramp up the frequency of the pulses for a soft start and ramp down for a soft stop.

Just wondering then if it's normal for the CNC machine to be programmed to ramp the stepper frequency up and down or whether that in practice is not usually necessary.

The alternative of course is to always keep the step frequency below the maximum starting frequency of the stepper motor when it's coupled to the load. Because then you don't need to ramp the frequency. You could though use different step frequencies (thus different motor spindle speeds) - just no ramping of frequency.

I note that whether you frequency ramp or not, the motor still does the same number of steps.