[me3000]

Oh, so it could be useful if a computer goes onto a closed network, or if it goes offline, yes?
Provided you're within range.

Imagine a cash register at a computer store, lets say Best Buy for example... I have seen BB have a cashiers terminal in their PC department before. So now an employee could infect both computers, allowing the cashiers computer to say interact with another PC in store that is on display and most likely much less secured(or even hide your own device in store). Then they can then communicate and the cashiers computer can receive simple commands...

You could have very simple commands that don't require much bandwidth. Extracting large amounts of data may be difficult especially with sound interference's much like how wifi can go to shit quickly with lots of other wifi traffic. It more less is just another possibility, probably not the best method in most cases, but an interesting possibility.