A very important point geffa makes. A decent amount of trading capital is required to make the whole thing work. Too many traders rely on T + 3 and are forced to sell within a certain time limit, as they don't have available capital to cover the purchase. Also, many people don't know how to take a loss properly, and remain in stocks that just keep going down, and then get out of them when they are at their bottoms. This is where insto's have the advantage, because they know this, and at times, artificially push a price down, and squeeeze these people out.
