In karate kihon and ido geiko we practice gedan barai, usually as a block against an attack to our abdomen (presumably a kick-shudders- or perhaps punch). Another application I have seen advocated, by myself as well, is as a wrist grab release technique. In both uses, the "blocking" hand is chambered near the collar bone and brought down smartly in a diagonal motion and stopping abruptly just before the elbow is fully extended. The problem with how karate kihon, ido geiko and kata are practiced is that these movements are often done without a partner and under the assumed operating environment of kumite. Karateka chop down with their forearm as they perform gedan barai, and much is lost.
The term "barai" implies a sweeping motion not a chop. Consider the sweeping motion of the strong arm in this video of Maul Mornie demonstrating knife defenses. The lead hand deflects the strike, the strong/rear hand sweeps down and across, and traps the attacker's hand against his body. Conventional karate wisdom holds that the lead hand is extended so that one might retract it forcefully and thereby speed up the blocking action. What is evident in Maul's video is that the lead hand is playing an active role in deflecting(passing) and checking an attack, rather than simply acting as a reciprocating limb. I would argue the Maul's downward pass, parry, trap and check is the proper gedan bari, where both arms have equal and important roles.
Done this way, a proper gedan barai accomplishes three things: it allows the defender to gain an advantageous position; it prevents the attacker from utilizing his lead arm; it allows the defender to sense through proprioception the attacker's next move. It is necessary, therefore that besides sweeping the strong arm down and across, the defender must push forward maintaining contact with the attacker's arm. The defender then checks the attacker's arm with his lead hand, freeing the strong arm to counter.
Is this too much gedan bari? Is the simpler version better? Personally, I think it makes for better karate.