When you buy your future home and take out a mortgage, you will likely be locked into a specific interest rate. However, you can refinance your mortgage to change how much you pay, and for how long.
The main advantage of refinancing is reducing your interest rate. If you have a variable loan rate, refinancing is a great way to get into a fixed rate mortgage.
People also refinance their mortgages to shorten the length of the mortgage term. The market average is a 30-year mortgage. When you refinance you can shorten your term to a 15- or even 10-year term.