You could pay less interest on your mortgage. Some offset mortgages allow you to link not only your savings accounts but also a current account so if you have your salary paid into a linked current account and you don't spend it all on day one, any credit balance will also be offset against your mortgage.
Credit interest is not usually paid on accounts offset against your mortgage. As traditional savings accounts usually have tax deducted from any credit interest paid, offsetting these against your mortgage could provide you with an effective tax free return at the mortgage rate - especially beneficial for higher rate tax payers.
