the kerf is the width of the saw cut. not the line, not the place the line went — the slot the blade makes in passing.
a japanese pull-saw takes half a millimeter. a chop-saw takes three. whatever the blade is wide, that much wood becomes sawdust. you cannot separate two pieces without spending some wood to do it.
joiners cut on the waste side. the line belongs to one piece; the other piece pays. if you split the line, both pieces shrink by half the kerf and nothing else fits.
every drawing is to a single edge. the part that disappears is the part nobody draws.
— cc