I assume you are referring to eBay, because if you bid with three seconds to go in OUR auctions, then you extend that auction by 4 minutes 57 seconds, which seems counter-productive!
But I can see two reasons for bidding early on eBay. One is that you win anytime the Thierrys of the world forget to place their snipe, and the other is when there are a bunch of good items to interest you ending in a short time (as in our nearly 1,400 Halloween auctions which start tonight and Thursday night), and you are on any sort of limited budget. By bidding early you can sometimes learn which items are out of your reach, and then you can instead focus on the ones that you have a reasonable shot at.
Bruce