Obtaining loot and selling it to the vendors throughout Ivalice is the primary means of earning gil in Final Fantasy XII. You can chain enemies together to increase your odds of getting higher quality loot and you can also sell loot in order to unlock items in the Bazaar. You can also purchase Grimoires / Monographs in order to improve the quality of items dropped from enemies (more information below).
Loot has no other use in the game besides being sold for gil and to unlock items in the Bazaar so do not hold on to it.
Check out the Chaining and Power Leveling guide for more information about chaining enemies together:
Check out the Bazaar page for more information about the items that you can unlock:
The last important thing to note is that you should make every attempt to begin purchasing the various Monographs/Grimoires that are available for sale to increase loot quality.
Each of the Grimoires become available for purchase from the Bazaar and increase the quality of loot you receive from destroying specific types of enemies. You can make them appear in the Bazaar by following the steps below:
These Grimoires will increase the value of the loot dropped by various enemies throughout the game. Chaining enemies remains a successful tactic for stacking up quality loot throughout the game so don’t hesitate to use this tactic outside of the three areas mentioned above.