Originally Posted by DocsMachine
Yep. It stores extra air between the output of the reg and the input to the dump chamber.
I can theoretically see that as maybe improving shot-to-shot consistency a tad, since there's now a bigger "buffer" of regulated air to pull from the moment the on-off opens up again, but there's a big difference between theory and fact.
That hole is after the on-off, since the teflon o-ring seals the dump chamber from the input. Not sure it would pull anything when the on-off opens up.