Some maintenance schedules include servicing the brake fluid at a certain mileage interval, some will suggest it every two or three years depending on the manufacturer. Regardless it should be changed and flushed through to keep the brake system stopping you and your family properly when needed. Today's cars have ABS brake systems and this adds another component to deal with if it fails. If your planning on keeping your car or truck long term it's a good idea to include this at service time.
Here is a great example of failed fluid- it started out clear & now looks like stew.
The other picture is test strips we use to verify condition. Judging by the color scale it is way past due.