Your mutual fund or other investment makes you money on the regular. What do you do with it? Well, you could go out there and spend it like a don. Or, you could set up automatic reinvestment, which means the money your investments make is put right back into your investment or fund to make you even more cash. Many mutual funds include this nifty feature, and the fine print might even tell you that don't have to pay commission when your cash is re-invested.