Sliding Doors

I first wondered about automatic sliding doors three years ago HERE.

Just now I walked by a Duane Reade on the sidewalk, and I triggered their automatic sliding doors. Why would stores have this feature on the outside? I can understand the inside; they're hoping you just bought a ton of shit and don't have your hands free so you can get the fuck out. But outside? Sure, maybe you got your hands full then too, but I don't think I've ever heard of anybody saying "no automatic doors to enter? Fuck that, I'll go somewhere else."

But even more importantly, how much money do they lose energy-wise by the doors constantly being opened by people walking by on the sidewalk? I mean, it's bad enough that people shopping are taking up energy, but people who aren't even coming in? Letting warm air out, cold air in? Wouldn't it be wise to stop this?