There's a lot of truth behind that. I used to watch Clark Howard's financial show (he's retired now). He said that for stores with big shopping carts, better purchase choices could be made if the customer only selected items that he could carry to the register. (The exceptions would be if you went in there for specific large items like a TV, appliance, etc., and/or you went in there with a list of items you needed)
When you have a big cart, there's plenty of room to throw in impulse buys. Hence, Clark's carry-only method forces you to make reasonable purchase decisions.
(PS.: I don't always follow his advice. Sometimes, it's big fun throwing carp that I don't need, into the cart.
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