The more people you take shopping with you, the more likely you are to come home with extra items you weren't planning on buying. You know... the items the kids toss in the cart when you aren't looking, or the ones they beg to try when you're just too tired to say no. Or how about the items hubby wants that you would feel guilty saying no to?
Shopping alone helps you keep a firm grip on your budget while getting some much needed, peaceful, YOU time... it's a win-win situation! :)