Do the pieces really fit? What about the kerf?

The line between the two pieces is drawn once and both pieces use it, so the knob and the socket are the same curve. With no clearance the laser cuts that line a single time (never twice), and the beam's own width, about 0.1 to 0.2 mm, is the fit: snug, and the knob stays put. Pieces > Fit clearance adds air between them for a looser fit, or for edges you will paint or stain. Kerf compensation grows the outside edges by half the kerf so the finished pieces come out at their drawn size.