As with any noise insulator, it may also be a heat insulator and keep more heat in the machine (depending upon your setup). The thin metal of the case may help dissipate some heat easier than one that has the noise insulation.

I've seen it on two machines. One was considerably quieter, and the temperature difference was negligible. The other machine may have been quiter, but I couldn't tell due to the noise of the large case fans (the temperature did not raise in it).

Speaking of looks, I had thought about spray painting the inside of one of my cases matte black, along with the racks. It has a window and a blue light inside and the black may make it look a lot better.

Dave