Most people can hardly imagine the resulting sound pressure level of their headphone from just any given voltage level. Arranging an equation with effectivity and impedance of the headphone in question as well as the voltage level are not an easy task for mental arithmetic …
„Will this headphone output be able to drive my cans?“
„Are the headphones (or even my ears) in danger to be damaged?“
„How much power is drawn from the headphone output at a certain signal level“
„Why is there such a big difference in sound pressure level when I use different headphones?“