I like the online builder as it gives me an idea where I am going to be sitting when I go in to order my next vehicle. I know that you can be more specific on the dealers system but I like to have a general idea where I am sitting before going to see the dealer. I hate them like the plague; and I used to be a new car salesman back in the day so I already know all of the tricks but it still pisses me off.
As has been said it is basically an inventory shopping tool. While that is frustrating to the small number of hard-core enthusiasts, it would be more frustrating to the masses to be able to build out a car they can't buy anywhere.
I don't know why people like the Jeep Build and Price tool so much. it only shows MSRP! I like the KBB.com build and price better. It shows MSRP, Invoice, and gives you a target selling price.
And by the way, the Build & Price tool will be wrong when it does come out. There will be options you should be able to select that you can't and stuff you can select that you can't order. And prices will not match the dealer system. And people will say it is because they did a bad job rolling out the JL but it is wrong every year.