I believe someone once said that if you exchange chips for a certain denomination of Legion coins (not the largest kind, not the smallest), then you can make a profit. Not sure if it's true though.
Legion coins, and NCR dollars are good if you are a low level character in need of fast cash, and if you have visted a casino. Take those coins and dollars, cash them in for chips, then cash out the chips for caps, easy money.
Coins are also good for coin shot rounds.
Both are good as a way of trading, if you want to save your caps.