I'm of the opinion that it actually takes me more time in the store to use it. Scan each item, sometimes fuss with the bar codes. Bag them in my cart ... it is almost assuredly longer than dumping things randomly in the cart and having a cashier scan them while a bag boy packages them up.

But.

It's invisible lost time, and the experience of not standing in the checkout line is t-rific.

I do get audited once in a while, but it's never a full audit. They check a few items at random and I'm on my way.