If an aircraft has been designed to have brakes, they're there for a reason. I'd get them checked out, because there is no point going flying with a known unserviceability that might be easily fixed.
An interesting thing happened to me last year; I was setting out on a night flight, and as we taxied out I checked the brakes. One was not working, so we returned, and took the other C172 instead. As we flew back at night along the coast, we suffered a partial engine failure; not enough power to keep height, but enough to vary the glide. Only one airport was in range; it had no lights and it was a cloudy night! We used the GPS on full zoom, and the altimeter, to land blind; and hit the centreline! However, we required maximum braking to stop or we'd have been in the swamp with the alligators.
You could argue that if we had taken the aircraft with a failed brake, we'd not have ended up in the one with the dodgy engine, of course; but in this entirely unexpected situation, the brakes rather came in handy.