Habitually setting the parking brake with the brakes still being hot and keeping it engaged for longer than until the chocks have been insterted results in degradation of some components, e.g. seals. Not really your primary concern if you are in a rejected takeoff situation with the possibility of evacuation right after. You should be more concerned with keeping the aircraft stationary (and in some airframe-engine combinations, e.g. A320F with IAE V2500 engines, it's certain that the aircraft will start rolling the moment you release the brakes).