probably a release thing - loosens the brakes so you can get your wheel out easily.
from Sheldon Brown:-
"To facilitate wheel changes, most high-performance road bicycles have a quick release mechanism that allows the brakes to be temporarily opened a bit wider than usual, so that the tire can fit through the brake pads.
Some brake quick releases are located in the brake levers, which is the best place for them. This type of quick release allows the brakes to work normally even if the user forgets to reset them after use.
Other quick-releases are located at the caliper or on the cable hanger. These must be manually reset after use, or the brakes may run out of travel. The better caliper-mounted QR's feature a cam which allows a variable setting. This is of use to racers who may knock a wheel out of true, because they can temporarily loosen the QR as much as it takes to get the bent wheel to clear the brake shoes"