“You have to open a door or window to let the pressure out of the room.”

“It needs somewhere to go.” I read this advice about optimizing a listening room on another forum. I’m an admitted neophyte but this sounded like a bit of silliness to me.  He said otherwise there’s nowhere for the sound waves to go and they will just bounce all over the room.  Perhaps he’s entirely correct.  What say ye? Where does the sound go?