A snipe bid is placed near the end of the auction, usually around 10 seconds before it ends, which doesn't give people you outbid a chance to come back and bid again.
There are very few practical reasons to bid on an auction days before it ends. That just gives other bidders a chance to raise your final price, or actually outbid you, causing you to lose auctions. However, most people can't be at their computer when every auction ends.
Let Silent Sniper bid for you seconds before the auction end. This program will save you money by lowering your final price paid for auctions, and can pay for itself after a few auctions.