My wallet allows you to exchange bitcoin for dollars or euros and Vice versa. Now there are pretty big jumps and it's a chance to earn. I constantly buy and sell my coins not even using the exchange.
Same with mine. If the value of bitcoin jumps, I sell my btc and when it goes down I buy bitcoin. If ever bitcoin would dump its value, I have a chance to buy bitcoin. It's like I get interest from buying and selling bitcoin.