I rinse to get everything warm and wet and smelling of tea. (Heheh...)The rinse water preheats my pitcher and cups, and it keeps the pot temperature high for the first proper infusion. I usually take a sip of it to gauge how long the first infusion should be, since I don't measure my leaves beforehand.
The best part, of course, is pouring the excess back over the yixing pot and watching it shine and steam. Even if it's just for show.
My only concern is that this step might be rinsing away the bulk of caffeine. (Yes, I'd actually consider that a bad thing.
) I'm interested in knowing if this is actually the case; but caffeine in tea hits me in different ways depending on what I've eaten, the time of day, the weather, etc... so I can't single out the rinse as a culprit. Anyone care to shed some light?