Haptic frequency has no effect on Rift S or Quest
Using the OVR haptic APIs, I can't seem to find any difference at all using difference values for the frequency parameter. From my experiments, only amplitude has any impact on the resulting haptic effect on Rift S and Quest, besides setting frequency to 0 which turns haptics off. So assuming a constant value for amplitude, frequency == 0 results in no haptics, any value of frequency > 0 results in identical haptics.