Jim,
if everybody only had one bid on ebay, then there would be (almost) no difference between sniping and not-sniping.
When you don't snipe, your maximum bid is matched up against everybody else's right away. This way, the price is driven up as you bid. Some people use that information to (re-)bid even higher.

When you snipe, you don't participate in these games. You just enter the maximum amount you are willing to pay, and since nobody will have time to react to your bid, it will not influence the price level (on a psychological level).

Redwoood