What is the point of duopolies? (TV)

I can understand in some cases like Viacom which owns CBS AND UPN how they would want to own two TV stations in one market. But why does a network like FOX (for example) buy Channel 50 in Chicago (A UPN) station. Fox will own Ch 32 and 50 then.

I see how TV2 Los Angeles would buy Ch 9 (LA) as they can change the affiliation of UPN from Ch 13 to Ch 9 when the contract runs out. But in the Chicago example wouldn’t the network be conflicting it own interests?

Hardly. It comes down to one thing: Money. FOX Corp will see a net increase in profits. All the revenue that’s coming into Channel 50 will now flow into FOX’s cashbox. In fact, I’ve also heard that FOX will be developing a news program for Channel 50, and this will also increase it’s overall ratings, giving it an even larger revenue boost. And it won’t even cost them much–they’ll be able to use Channel 32’s news resources…spreading the cost between two stations.

Not bad, eh?