Going to your own bank is simple, but it only shows you that bank's loans. A mortgage broker, also called a mortgage adviser, compares lenders for you, from the major banks to specialist non-bank lenders, and manages the application through to settlement.
The difference shows when your situation isn't straightforward. Lenders treat self-employed income, rental income, smaller deposits, new builds and credit history differently. Knowing which lender suits your mix can change how much you can borrow, the structure you get, and whether you're approved at all.
Brokers are usually paid a commission by the lender when your loan settles, so many borrowers pay no fee. Financial advisers must put your interests first, and must tell you up front how they're paid and about any fees or clawbacks. Ask to see this in writing.
A broker also saves time. One conversation covers several lenders, you apply once to the lender that suits you, and each refix comes with a check across the market, not just your own bank's offer.