I think the thread starter mean sound dampen the sheetmetal using Dynamat and the like...
The point of that is to reduce resonating noise from panels, stopping low frequency humming etc.
A well damped automobile can give you 2-3x more headroom equivalent of tripling your amplifier power in audio systems.
You'll still hear ambient sounds, horns, etc...
To put it simply, imagine your daily Civic sounding like a high end Lexus/Benz cabin.