During the last half of the 19th Century when the machine age brought about mass production of all things including furniture, the use of dowels was introduced to make woodworking joints. It speeded up the joint making process because machines could now do what men's hands did in the past. And for all the curved work of the Victorian era, the joint was practical, eliminating the short grain in the tenons. However, this joint has an inherent weakness—it relies on the glue for the integrity of the join. Previously, the mortise-and-tenon join only needed the glue to keep the parts from coming apart but provided excellent rigidity to the entire assembly without any glue at all. Dowel construction, on the other hand, provides only a small fraction of that rigidity. The problem for the restorer is in repairing and regluing these joins.
Dowel joins often suffer from poorly mating surfaces. Due to shrinkage, the geometry of the frame will likely have changed and things that once mated perfectly now have gaps in them. When dowels break, the parts still glued in their holes have to be drilled out and new dowels made and inserted. Often the parts being connected are out of alignment unless a little wiggle room is provided. All of these factors call for the use of a gap filling adhesive. Against conservation dogma, I often use epoxy to glue these joins. A big benefit is that no original material needs to be removed except broken dowels. Even the hide glue can be left as a barrier. Also, the epoxy is a much stronger adhesive for less than perfect joins. The down side is that removing the epoxy or taking apart a solid join is difficult. For furniture that is not antique this is not a particular problem. On antique furniture, this approach is controversial, yet in my estimation warranted for furniture that is to be used. Weak joins will eventually be stressed and fail, sometimes with the consequence of other parts becoming broken. By making a strong join, the frame can better resist the strains of daily use.