Well money and bartering are very closely linked. Say you like to paint, for example, and you wanted to try living on that (heh good luck) even if you paint a lot of very good pictures, real high-society art type stuff, then your currency (paintings) are really only any good to people who specifically want paintings. If someone else had something you want, like maybe a good affordable car or something, and they'd only accept jellybeans as payment, you'd be completely out of luck, but because we can trade for the universal currency (well ok not exactly universal, but everyone at least recognizes money as having value in some form or another) you can trade someone who's interested in paintings, for money, and KNOW that that car dealer is going to accept that money (and not demand the jellybeans that you just couldn't come by) and you'll drive home happy as it were. It's just so much more convenient!
Besides, a barter society is a cash society. . . Imagine that you were a luxury car salesperson, now it's going to take a hell of a lot of jellybeans, or computer parts or, whatever the heck you'd like to trade, to get you a luxury car, you'd have to bring this stuff to the dealer in wheel barrels, and then he'd have to figure out where to stash the damn stuff while he looks for either some use to put it to or someone else to trade it to. It's just very inconvenient. A small light weight currency like our paper money and coins is much more efficient, but even better is when nothing actually changes hands at all, credit, debit, checks, they’re all even better because for one it’s much harder to lose than a physical currency, and it’s easier to determine it’s value and authenticity.