That's a great maintenance item to remember.
It is possible to boil brake fluid. It absorbs moisture through the hoses and seals. When is discolors, it is junk.
Long time ago on a roadrace bike, I had cleaned/adjusted/flushed/safety wired on a CBR600 I had. After 5 minutes of hotlapping, and at the end of the backstrech (Nelson Ledges, easy 120+), went to go for a handful of front brake and got nuthin' but lever into bar. Needless to say I took a trip through the grass, but kept it rubber side down somehow.
Big dummy me never bothered to change the "coffee" in the brake system and it boiled in the calipers, causing an instant air bubble and no brakes. Brakes came back like magic when the rotors cooled (and after I cleaned out my shorts). It's a feeling you never forget (brakes and soiled shorts both).
That stuff is so cheap, and nobody ever thinks to flush it annually. Well, almost nobody. It will keep the brake guts from getting that rust/funk growth too.