bb,
on the b777, when the gears are raise, braking is apply to the wheel to stop the spinning. if the airplane is going to be despatch with a brake deactivated by capping the hydraulic line to the brake (this could be due to brake failure on the particular wheel or its antiskid module, etc), the the gears would have to be left down to allow the wheels to spin-down (2 mins). obviously, performance penalty would have to be applied (reducing takeoff weight) in the event of an engine failure after takeoff.
hope this helps...SR