I agree with Dyna. Its the thrill of the chase, there is the down if you don't win, but there will always be another one.
TBH though I don't see the point of these tools, just put in the maximum you are prepared to pay for the item and see what happens. If no one else is prepared to pay that then you'll get it cheaper, if they are then you won't win. Most times you will only lose an auction by the next minimum bid amount, but thats not to say if you had bidded that much extra that you would have won, you'll never know how far the other bidder was prepared to go.
They're awesome for when the bidding ends at 3am, or when I'm work!
They're also great for keeping the price down. If I bid early at my maximum, there's always some pleb who changes his mind and ups his maximum (as if me bidding on it somehow makes it more valuable to him/her). If I snipe it, they don't get a chance to do so. If they've set their maximum correctly (i.e. the actual maximum they want to pay), and it's mroe than mine, they'll win anyway, so no problem.