GIXEN submits your eBay bid just before the listing ends, saving yourself from a bidding war.
Ever use eBay? Basically the idea goes you bid the price you want, and other users do the same so the price gets pushed up.
With snipping service, they bid for you in the last few seconds, so you still participate, but give other users less time to increase their bid. The main purpose would be to avoid a bidding war, or to avoid pushing prices up on that item no one knows but you searched so hard for.
GIVEN allows 10 scheduled bids for free, which should be sufficient for the average user.
A note of warning though - always think hard, and do research, when a site asks you the username and password for another site. Think about it and only use GIXEN with your eBay password if you trust them.
Many of these exists for years, much more trust worth ones come in forms of firefox plugin with unlimited snipping. However don't see what money you save here, you also can be outbid by other's higher maximum bids anyway, good tool but not a bargain.