Too tight will keep the valve from closing when the engine is warm and it will be harder to start warm than cold. Unfortunately, an exhaust valve that doesn't completely close can't transfer its heat to the head and the valve will burn like it's being held in the flame of a torch. It doesn't take long from hard to start when warm to damage being done. Too loose is rare in shim and bucket valves as they close up when they wear but the chief symptom will be noise as the bigger arc the cam lobe goes through before contacting the bucket becomes more like a hammer.
