I don't think there is any harm to keeping the brake on overnight. If there is a stiff prevailing wind, I find it useful to orient the main rotor blades parallel to the wind, then putting the brake on. There is a lot less flapping than when the blades are locked perpendicular to the wind. With the r22, I used to tilt the blade down then spin the lower end around so that is was over the tailcone, then lock the brake. This kept people from reaching the other "high" blade and pulling it down. This is less of a problem with the r44 since the blade is so high that you have to jump to reach it.
One time at an off airport location, I returned to the ship to find a teenager demonstrating to his friends how the main rotor blades turn when you move the tailrotor. Luckily the rotor brake was not on full, otherwise the tailrotor drive shaft/flex couplings could have been damaged, or the tailrotor blades could have been bent. After that incident, if it is not windy, and I am off airport, I leave the brake off.