Steppermod vs freqmod

Hi people,

Would someone mind explaining the practical differences between Steppermod &
Freqmod when running stepper motors via step/direction.

I have both versions (bdi install) setup on my mill and I can't really
notice any difference in performance.
What is the advantage of one over the other. I understand that freqmod uses
more PC resourses.

Just curious, as both seem to work OK.

Thanks

TimS