Trade out an ARM. If you plan to be in your home for a while, refinancing can get you out of an adjustable-rate loan and into a fixed rate one. You could also refinance into another lower-rate ARM.
Combine two loans. Some homeowners refinance to combine a first and second mortgage into one low-rate loan.
Cash out on some equity. If you have enough equity, you may be able to tap it to consolidate debts or pay for home renovations.