What's the point exactly?

What is the point of this thing to the left? It's been in effect, indicating the 'threat level' in the US since March 2002. Most of the time, it's at Yellow (Elevated). Once in a while it's Orange (High). Rarely is it at Red (Severe). But it's never below Yellow. I wonder what it would take to get to Blue (Guarded) or even Green (Low)?

What's worse is that there's more than one scale. There's one for the 'National Threat Level' - which right now is Yellow. Then there's one for domestic and international flights - which right now is Orange. The Homeland Security site says "Raising the threat condition has economic, physical, and psychological effects on the nation; so, the Homeland Security Advisory System can place specific geographic regions or industry sectors on a higher alert status than other regions or industries". Which means what exactly? What's the difference if the nation is at code Yellow, but the planes are at code Red? I wonder how much money is being wasted on this nonsense?