Here in Thailand they do the same thing. One difference though is that a lot of places give you a parking garage ticket even though they don't charge anything to park. They will write your license number down on the parking slip and give it to you as you enter. You are supposed to give it to the attendant when you exit.
I asked Tim about it. The rational is that it is to deter theft. You are supposed to take the slip with you and not leave it in the car. So if someone tries to exit without the slip, then they have to show proof that they in fact own the car. Personally, I believe it actually has to do with a bigger trend here in Thailand. Sometimes I think people here copy "best practices" of some other company without necessarily understanding why the practice doesn't make sense in their particular situation. All these other parking garages hand out slips, so I guess we should too.
While labor is not terrible expensive here, it can add up. A company can spend tens of thousands of dollars a year distributing and collecting parking slips that really don't serve any purpose. Today at Central there was no-one to give me a ticket when I arrived. When I exited, I told the guy in my poor excuse for Thai that no-one gave me one. I was waived on my way.
In the last six months or so, a bunch of companies have been moving away from this practice. The grocery stores have now installed cameras at the entrance and exit. That way if a car is stolen, they can look back on the video to try to find out what happened. My wife's company finally eliminated the practice. When she proposed it, her managers argued with her that it was necessary to protect against theft. She pointed out that they printed on the ticket that they weren't responsible for theft.
Its good to see this change. Its not a huge deal, but sometimes its a pain in the butt to dig through pockets trying to find that little slip of paper.