Garrett Hack replies: In general I don’t use loose tenons or dominos because they are often weaker than an integral tenon. Loose tenons need a good fit into the end grain of one part and the long grain of another, all at the proper orientation—not so easy if you have tried it. Where these joints do make sense is for angled joinery, where an integral tenon might have weak short grain.
Dominos work well for low stress joints where alignment of the parts is more important than strength, for example a runner joining into a drawer blade.
Richard Oedel replies: Dominos, when appropriately sized, work wonderfully. But often they don’t get used or glued correctly, so the joint strength suffers. I’ve used loose tenons made with horizontal boring machines and very tight tolerances and have had great luck. I’ve also used a lot of dominos, but mainly on sheet goods where they excel. The larger domino allows larger, more robust joints, so think about using that for the larger pieces.
In general, I try to have a tenon 1/2 to 2/3 of the width of the piece if I can make that happen. Where I have seen dominos fail is when they are undersized.