In theory you are not paying the bid ask spread since buyers and sellers are agreeing at a single price. Of course, this assumes the specialist(for NYSE stocks) is not taking a few cents off your pocket, but it should be random whether this will hurt you or benefit you since sometimes you will be on his side Thoughts?
Well Mr Daal in a downtrending bear market; open price isnt likely to be the best@all Nor is the opening price in a bull market likely to be the best; but more likely than in a bear market.But again ,there are plenty of exceptions Of course in the unlikely even of a huge gap [like earnings against the trader/investor, an open sale could be wise. Bright Trading Co may differ AMR, DAL,LUV open price after SEPT 11/11 was best cover if short; long daytrade[long trade to open], again open price wasnt best at all[unless you count 20/20 hindsight, i dont count it on that trade.]...Because they easily could go down much more.
The open/closing auction are specially useful if you are an institution and you need to execute very large blocks of stock.