Ebay question: Why bid on an item with no intention of paying?

I know some people change their minds or find they cannot afford to pay the winning bid amount. What I’m in the dark about is the whole bidding on an item with a bogus account. What purpose does this serve? Is it to drive me out of the market? Is the person just bored? Lastly, how long do I have to wait after the close of the auction – given the fact that I’ve sent emails and received no responses – to re-bid or offer to someone else?