The one scenario where layaway makes sense financially is if you are buying an item on sale but you can't afford it immediately. I could see how you might want to do all your Christmas shopping on Black Friday but you don't have enough money to pay for everything. You get the discount but layaway gives you an extra period of time to make the payment.
I think I already mentioned it, but it is worth repeating: Walmart's layaway will not be available on Black Friday.