There are many uses for butterfly or bowtie splines. They can be used to reinforce and decorate frame and box miter joints, or even to repair a split in a panel or table. They can be used in breadboard ends. This allows the panel and ends to move independently, but the dovetail shape keeps the end tight to the panel.  Use a 14° dovetail to cut the receiver piece first, then use this bit to cut the butterfly piece for insertion, sizing as needed. Blend in or contrast as you choose. Carbide tipped.