For most Americans, buying a home is one of the biggest and most important investments they will have made in their lifetime. So, it's a big deal and it is a long-term commitment. But as we all know too well, the financial profile of a person may change over time. If you own a home, it's possible that after a few years, your credit rating, your income, your tax bracket, your debt ratio etc may be very much different than when you first purchased the house. Add to this possibility that the state of the economy may also be very different than when you made your initial purchase (or refinanced last), as interest rates and other societal conditions may ave changed.
The right time to refinance is ultimately a very personal decision - one that comes after deep assessments of where you are financially, the particular term of your current mortgage (adjusted versus fixed), your current mortgage program (FHA, VA, Non-conformaing etc), the interest rate of your current mortgage etc.
There are many reasons why it might be advantageous for you to consider refinancing, but it is not always as clear-cut as many might think. Of course, if the current rates are lower than the interest rate on your loan, and you can qualify, then that's an easy decision. But often it's not that simple, as there are many other factors to consider when evaluating whether or not now is a good time to refinance.