The sliver of sleeve that peeks out from a suit coat acts as visual punctuation. It gives the arm a definite ending point and creates balance within the ensemble.
Approximately one-quarter to one-half inch of sleeve generally shows past the coat sleeve. Allowing the sleeve to extend farther may make the coat look too short, while showing less sleeve creates the opposite effect. The shirt sleeve generally ends at the wrist bone, with a cuff snug enough to keep the sleeve from sliding on to the hand, yet loose enough to allow freedom of movement.