Pretty much every JRPG will have a stereotypical boss that charges for one turn and rapes you the next turn unless you defend, so that one battle can justify the existence of the defend command.
In general though, defending is only useful in a battle system that incorporates and exposes the concept of initiative in a way that's actually meaningful (e.g. the Grandia series, maybe FF10). If you can see when and whom an enemy will attack next (and they actually do significant damage), you suddenly have a legitimate choice to make: do I attack and take full damage so I can take this baddie down faster, or should I defend this turn and let my other party members take care of him? Not defending in a Grandia game is a good way to die pretty fast.