Forex Swap rates are important to know if you are going to  hold a position more than a day.  Why? Because you will have to pay the swap rate or you will get paid on the swap rate depending on your position size.  Here is a good site that keeps live updated Forex swap rates 

A positive Forex swap rate relative to your position can be a valuable thing if your positive swap rates coordinates with a Forex trend that you are riding to large profits.