Assembling workbenches in the old-school manner is a nail-biter.
If the drawbores are too close together, then you drive the peg in and nothing happens. The tenon isn’t pulled into the mortise. You start looking around for your framing nailer.
If the drawbores are too far apart, you drive the peg in and it explodes when it hits the tenon.
Either way, after days of work, your bench is in peril.
When the drawbores are just right, then the joint comes together beautifully. The peg is hard to move, but it moves. And the sound is different when you pound the head of the peg. With a bench like this one, made of Douglas Fir with 2-1/4”-thick tenons, we are using about a 3/16” offset between the tenons.