Bolts are used in robust structures on their own if no requirements are set for the rigidity of the joint. Bolts are primarily used for binding the structural parts into place while the forces are transmitted from the wood by means surface compression.
In a notch joint, the bolts may – if the wood is shorn – prevent the ultimate breaking of the entire structure. In a doweled joint, the bolts hold the connection together, but they can also receive some of the shear forces of the joint.