I earn my living installing wood trim on doors and windows as well as crown moldings and molded wall panels and the like. When two pieces of trim come together at a corner they are cut, or mitered and fastened. The tighter the miter the better the carpenter. My boss is fond of saying if your paycheck can fit between the miters, you can’t keep it.
Pinch dogs are simple u-shaped pieces of steel that are driven into the wood across the joint. They draw the joint together until the glue dries. They are also useful for clamping boards together edge to edge if you don’t have bar clamps long enough to reach the outside edge.
I have gotten used ones on EBay at substantial savings.