Unless you have plate proficiency anyway. Even then it's a feat for the same damage than 1handed BS and -1 AC and -2 Ref compared to 1handed BS and Shield.That One Guy said:<throws down the snark>
The tradeoff... a feat to use a bastardsword one handed so you can hold that shield, or do you go two-handed w/ the greatsword and use that feat to snag something else... like I dunno'... plate? Some people'll say AC all the way, others're pro-putting the stabbity end into things.
With the limited knowledge we have at the moment, 1handed BS+Shield seems just superior greatsword or 2handed BS