Timber members should neither be too large or too small and the joints should stay tight over time. All wooden beams will shrink & check as they dry - it is part of the unique nature of timber framed buildings. The element that defines a professional timber framer is the way in which the joints fit together. A good joint will stay tight and strong for generations.
Most of our joints are pinned together with 1-inch hardwood pegs. The geometry of the joint itself carries most of the structural load, and the peg holds the joint in place. When loads are extraordinarily large or when aesthetics call for it, we use heavy steel plates & bolts, as in the Vermont Teddy Bear Company frame shown below. All of our joints undergo in house engineering to confirm their strength and integrity.