When Maureen and I visited Paris a couple of years ago, we noted that whenever we paid for our meal by credit card, the server would bring a hand-held device to the table and process the entire transaction right there. In other words, the credit card never left the table (nor our sight).
So, this method has two obvious advantages, the first being that you keep control of your credit card, and the second being that you don't have that additional wait for the server to take your card away and then return with the authorized receipt. We liked this approach very much from the first time we encountered it.
So the natural question is, why don't restaurants here do the same thing?