You probably noticed a little more "edge" to the engine sound. Removing the box also improves air circulation, but it's probably not measurable.
BTW, one can use a plastic pipe cap and a hose clamp to plug the hole. Get one that fits inside the hose.
Ed in San Jose '97 540i 6 speed aspensilber over aubergine leather. Build date 3/97. Golden Gate Chapter BMW CCA Nr 62319.