Budding is often used because a single scion bud is inserted into the rootstock to produce a new tree. Also, with budding, many trees can be produced from a stick of bud wood that has different sized buds.
In contrast, a piece of scion wood with two buds is used in grafting, and the diameter of the rootstock and the scion piece must match precisely to form a union. Thus, fewer trees can be propagated by grafting as compared to budding.
Answer provided by Dr. Michele Warmund, University of Missouri.