A high port, in addition to giving the tongue relief, also places pressure on the palate of the horse's mouth when the reins are pulled. Used improperly, a high ported bit can be very painful or damaging for a horse's mouth.
Ports that are solid, rather than made of a U shaped bar are actually called spoons or spades, although they look somewhat similar. These do not provide tongue relief. The spade or spoon may include elaborate rollers or "crickets", double mouthpieces and are only used on very well trained horses by skillful riders who understand the severity of the bit they are using.