If you bid early, some idiot will come along and put in 30 bids, raising the bid price $1 at a time, until he finally exceeds your bid. If you wait (along with everyone else) and bid at the last second, the idiot doesn't have time to do that, and you are likely to bid higher because they don't have time to creep up the bid.
He would have to be an idiot to do that, since eBay will do it automatically for you. If you enter a bid much higher than the current winning bid, eBay will post a bid for you that is only a couple of dollars higher and ratchet up your bid only if someone else ups the bid.
Sniping manually is a good way to give yourself a heart attack. I used to do that, but now I just enter a bid that is the highest I would reasonably pay for an item a few minutes before the auction closes and go back later and check to see who won or just wait for the email notification.