"there's no such thing as a closed loop system"
That's not incorrect though; you're still needing to shed the heat energy SOMEWHERE. Thermodynamics alone dictates that basic fact. You may not waste the cooling solution but all that excessive GPU heat is going to need to go somewhere - and the only place it ultimately goes is right into the environment.
Ever stand a bit away from a campfire because you got too warm, only to have the wind hit it and blow hot air over you? Same thought exercise applies here.