Peter,
You are correct in that it balances the brakes. It prevents too much braking at the rear wheels, and thus hinders them from locking.
Seems like most racers replace the factory one for an adjustable one.
Here's a great web site by Mike Valant, look at the pics of the race car, and see the adjustable brake bias in the cockpit.
Might E-mail him for the correct part to buy.
http://www.mev.cc/