I stopped by my local nationwide bicycle shop awhile back and was interested to see that they are dedicated Green Energy enthusiasts, declaring that they "purchase renewable wind energy credits that will offset 100% of the electricity used by all of our retail stores."
That was interesting because I was heavily involved in generator interconnection and I knew that there was no wind energy in my state - none, zip, zero, nada - and only one green energy applicant, not even online yet. They were buying Green Energy credits from elsewhere to offset local use.
So that's when I developed my own brilliant business plan (and here is where we depart from reality into satire). I decided to use the credit bit to start selling bicycle credits. Here's how it works: you decide (or your doctor states!) you are too fat. You must lose weight. But you don't like exercise; it's too hard, you get sweaty, there's no gym nearby, and it's too much work anyway. So what you do is buy credits. You sit on the couch and eat Cheetos, while I go ride my bike, which I'm going to do anyway. I sell you the exercise credit, and you give it to your doctor to show him you're doing your part to be healthy. I get paid, you get to relax on the couch, and everyone feels better. Especially me if I'm getting government subsidies for my new bike anyway.
Now back to reality: Locally, the power grid is a complex network of interconnected facililties - generators, lines, transformers, etc. It's not one simple linear thing. Everybody puts into it, everybody draws out of it, almost like the internet. The local utility grid planners/operators work to ensure that power flows freely and no individual piece gets overloaded. They try to plan for the worst contingency during the one peak load hour of the year, but remember, it's not a linear system. There are a thousand different variables that make it difficult to determine where the power is going to go, and those variables are constantly changing (see Blackout 2003). So we mark the overall trends and try to do the least amount of work to get the most amount of system security.
In reality, some wind farm in Wyoming has virtually no impact on load in Peoria. I confess to being a cynic and not a fan of global planning for local solutions, but energy credits make some feel better (and carbon credits too, and fat credits).
(Now for my real soapbox - I do not believe conservation can ever keep up with our growth rate, and I do not believe renewables can replace fossil fuels with out massive government subsidy, barring discovery of cold fusion or perpetual motion. Answer: Nuclear, baby!.)