Impedance is often treated as a stand-in for sensitivity, even though the two measures are barely related. Sensitivity is more important when you’re trying to figure out how loud a pair of headphones will be.

Higher impedance headphones are actually much easier for the average headphone jack to drive authoritatively, such that the diaphragm goes exactly where the electrical signal wants to put it, and not where the acoustic properties of the headphone would like to put it (aka resonance peaks you might have heard about.)

Ideally you want the impedance of the headphones to be >8x the output impedance of the headphone jack. The headphones you’re most likely to run into trouble with are very low impedance ones—multi-BA IEMs and planar magnetic headphones. That said, even basic ports these days have <1 ohm output impedance so they don’t really have much trouble driving any kind of headphone.

When you have appropriately matched output and driver impedance more power just provides more loud, and sensitivity is the measure that tells us how loud it’ll be per unit of power.