Just finished watching Kelly's Heroes and noticed all the netting being used. I've also seen it used elsewhere. What purpose did it serve exactly?
With respect to bases, it was done to break up the shapes of both buildings and the structures of the bases themselves to make it harder for enemy planes to target them. An excellent example of this would be the American airplane manufacturers such as Boeing's plant 2 and Lockheed's Burbank plant.
This 1942 "Camouflage Memorandum" and the series of US Navy "Passive Defense" manuals from 1941 and 1942 should show some of the philosophies behind the netting and building camouflage. The key thing to remember is that it wasn't designed for CLOSE enemies but enemy bomber formations at altitude (10-20,000 feet).