In most RPGs, rewards from battle are usually handed out simply for beating an opponent. Most RPGs will reward the player with a fixed quantity of experience points and money based on what enemy he just defeated, with a completely random chance of finding an item after the battle. However, there are some RPGs that have experimented with rewarding the player based on how he performs during battle, which has produced some very interesting results.
This practice is actually fairly common among action games, particularly ones with some RPG elements. A good example is Devil May Cry, which rewards the player for maintaining a high style rating by rewarding the player with a much greater number of Red Orbs, which can be used to purchase items and equipment upgrades. Similarly, Drakengard rewards long attack chains with health restoring orbs and other power-ups. However, it is much rarer to see this practice among RPGs.
One such example can be found in the action RPG Megaman Battle Network. In every entry in the Battle Network series (including the two Star Force games), the player is given a busting rank at the end of each battle. This busting rank goes from one to ten, with a special rank of S for a performance better than a 10. It is based on a number of factors: how many times the player took damage, how quickly the player defeated the enemy, if the player deleted more than one enemy in a single attack, and so forth. Busting rank does more than just tell the player how well he fought though; it determines what prize the player receives at the end of combat. A high busting rank means that the player will have a higher chance of earning a powerful battle chip at the end of combat, while a player with a low busting rank can expect to receive a piddling amount of money. So, the game encourages the player to fight every random battle as efficiently as possible. As a result, common strategies in the Battle Network series involve trying to wipe out every enemy with a single opening move.
The PS2 RPG Ar Tonelico also rewards the player with different items based on battle performance. Every enemy in Ar Tonelico has four items that they may drop, based on the maximum synchronization level the party achieves during the combat. A player who fails to raise the synchronization level will only acquire the enemy's least valuable item after the fight, while a player who manages to raise the level to it's maximum will receive all four of the enemies' items after the fight. So, the player is strongly encouraged to put in the effort to maximize synchronization in most fights. Furthermore, performing certain actions mid-battle (such as casting powerful spells) rewards the player with Dive Points, which can be used to augment the powers of certain characters.
While Final Fantasy X stays true to the more established rewards scheme for the most part, it does give the player some rewards for doing well. If the player manages to do significantly more damage to a monster than it's max hit points, that monster will be Overkilled, and that monster will be much more likely to drop any rare items in its drop table.
I like systems such as these for two simple reasons:
1) These systems give the player something to do during regular battles other than mindlessly killing monsters. If the player is rewarded for killing monsters faster, then the player has the goal of killing every monster more quickly. This has the overall effect of making routine battles more intellectually engaging, and thus more fun.
2) These systems give the player the ability to strive after acquiring an item, as opposed to just relying on dumb luck. For example, someone hunting after a battle card in Megaman Star Force can rebuild his deck to take advantage of his target's weaknesses in order to increase his odds of getting an S rank and earning his prize. This allows for item hunts to be much more interesting than the mind-numbing farming that occurs if an item is just dropped randomly. It also makes the player feel that he earned his reward based on his effort, as opposed to mere good fortune.
I wouldn't mind seeing systems like these become more common in the future.