Hi Erikfsn,
From my experience the biggest difference is that the Domino is the very best method I have found in over 40 years of designing and hand crafting fine furniture to control wood movement in solid woods. It is vastly superior to biscuits which only sort of strengthen a joint but will do ok at aligning two faces. When not glued, or glued only into one side of the joint, the domino positively locates two pieces in two planes if all the domino mortises are cut at the narrow setting. When not glued, or glued only into one side of the joint, the domino positively locates two pieces on one axis while allowing them to move in the other axis if the domino mortises are cut at a wider setting.
When glued, most all of the strength of any loose tenon joint comes from the face of the mortise and tenon and very little from the edges so side to side fit is usually not very important except for initial alignment. The domino sinks much deeper into the adjoining work pieces than does a biscuit, thereby moving the bending moment over a longer dimension. When the joint is stressed one side is placed in tension while the other is placed in compression. The compression side is kept in registration by the strength of the domino tenon while the tension side is strengthened by the glue joint along the fact of the tenon.
The magazine articles "testing" joints that seem popular right now all test a 90 degree, one sided joint. That is, they join two pieces of wood at 90 degrees, then apply a force to the end of one while holding the other leg fixed. They measure the amount of force required before the wood fractures and declare that a good analog for real world joint strength. That is neither a good test nor a good analog from my experience. Wood joints are seldom if ever one sided. They most always work in combination with other related joints to transfer forces around the object such that no force is sufficient to fracture the wood itself.
Case in point, a rail, stile and panel construction. The joints where a rail and stile come together are often just the stub tenon formed by the tongue on the rail fitting into the groove on the stile. That is usually something around 10mm deep so there is not a lot of glue surface. Yet cabinet doors built that way can last for decades if not centuries. The key is that the bending force trying to tear the rail away from the stile on one of those joints is transfered to the other three joints in that same panel. Make that same door with butt joints reinforced with biscuits and it will be much weaker since the bending force will try to rip the biscuits apart along their center line and along the long grain to end grain glue joint where they are weak. With a loose tenon, like a domino, the same force is trying to pull the tenon out of the mortise along the long grain of the tenon where it is far stronger. Very little of the strength comes from the end grain to long grain glue joint.
I actually make such panels/doors by adding a domino loose tenon to reinforce and locate the short stub tenon (10mm x 10mm in my case) joint. I cut those domino loose tenons 5, 6 or 8mm in width depending on the size of the door cut inside the tongues on the rails and grooves in the stiles thus forming a haunched M&T joint. This construction is so strong that I make glass doors this way with the outboard joints glued and the hinge side joints held together without glue only by long trim screws. That way there is no ugly glass mold on the back side of the door yet the glass can easily be removed by simply removing the trim screw and tapping the hinge side joints apart.
I know people who will disagree and will strongly support biscuits or dowels or traditional M&T joints and point to the one sided magazine "tests" to validate their POV. I also know people who build chairs using biscuits at the critical back to seat and seat to leg joints but I would never be able to sleep at night if I put that time bomb into my customer's home.
Since the day the domino first came into my studio it has changed fundamentally how I design and build fine furniture. My wonderful Lamello biscuit jointer now sits idle most of the time and is only used to cut hinge mortises for the Lamello hinges which I really like. I hope these observations help.
Jerry
