Yes. It shields the innards from RF both internal and external. I would posit that a shield-less icebook would get crappy wifi, have audio problems from the audio cable inducting nearby signals and possibly even RAM problems. The shielding also acts as a low flow heat sink because it is made out of aluminum and pulls some of the heat away from the system board in a passive manner. It's primary purpose is to shield, but it is my educated guess that it also acts as a heatsink.

Why do you ask?