Refinancing your mortgage allows you to access up to 80% of your home equity.
This allows you to possibly do the following things:
Use funds to consolidate debt. Why have high credit card debt at 20% or even higher when you can roll it into your mortgage at a much lower interest rate?
Extend your amortization, reducing your monthly payment and creating cash flow.
Improve your credit score. High balances on credit cards and lines of credit can negatively impact your credit score.