I never felt the need. Are you thinking of controlling heat? or noise?
I think I want the heat to release rather than be held in (which is why some cars have louvers). Good paint should not be affected by heat.
The noise (engine, notably valves) is part of the experience for me. The bonnet itself should not rattle if all the rubber bumps are in place and adjusted.
The only advantage I can see (in retrospect) is that it might have reduced the damage when a fan blade let go and tried to exit the engine bay upward.