In short, there are a lot of parts to your brakes. All of these parts should be checked at least once a year. Brake pads wear out. Brake fluid can leak, or absorb water from the air and become less firm. Hoses can crack.
You want to be sure to get brake pads replaced before they wear out entirely. Your brakes will still work, but the caliper will be grinding on the rotor. That makes the rotor wear out faster, and you'll have to have it replaced or resurfaced more often.
If your brakes feel mushy, or chirp or screech when you stop, it's past time for a brake inspection. Visit any of our stores soon for brake service.