If you've got a couple people going back and forth on an item, the price can really skyrocket. If you bid early, you're inviting people to push your price up and also indicating that the item is worth bidding on.
This is the idea, and apparently true. What this means is the purpose of sniping is to avoid giving non snipers a chance to reconsider. Sniping does NOT protect you from other snipers, who bid rationally at the last moment, sniping protects you from the NON snipers who keep raising their max bid because they think the point of an auction is to 'win'.