One real plus for AS is the ability to put in a snipe days before the end of the auction. If you use the proxy bidding system on eBay and later have potential "buyer's remorse" prior to the end of the auction, all you can do is hope someone else will outbid you. You could retract your bid, but it is frowned upon
, and you must leap a number of hurdles. If you are using AS, you can always go to your snipe and change or delete it until around ten minutes before the end of the auction.
One other plus is that you don't get sucked into a bidding contest, just to satisfy your ego, and later win something you paid too much for.
And finally, unless the item you want is something extremely rare that you absolutely need immediately, (or you happen to know more about its value than anyone else) you can always wait for that or a similar item to show up another time and try to get it for what you believe to be its true value to you. Sorry for the wordiness, just wanted to give you lots of tips (that have proably already shown up dozens of times in other topics or forums.