Zapster - You just haven't thought this through. If you said you wanted to have entry orders in opposite directions, that would be what some calll a bracket trade - if the FTSE100 price is now 5900 and you want to catch a move either go up or down, you place an order at 6000 to catch an upward move and a sell order at 5800 to catch a downward move. Many SB firms allow OCO (one cancels the other) orders for this type of system so that if your buy at 6000 is triggered, your sell at 5800 is cancelled, and vice versa.
But you were originally talking about positions, not orders. If price is 5900 and you buy at £1 per point and simultaneously sell at £1 per point, your profit (and loss) will always remain zero, no matter how far price travels and no matter in which direction. If it goes up 100pts you make £100 on your long and lose £100 on your short, so what's the point?
In reality, you would lose the spread on eventually closing each trade, plus overnight finance charges if you're keeping open Rolling SB positions.
Eventually, you know, you have to take a risk in this game.
True, As soon as you open the long in this situation your position is -£1. Then you open the short and that position is instantly -£1 also. Your account balance is now -£2 and you havent actually gone anywhere.
I think it can be usefull for example if you use another SB to potentially hedge a position if your original provider is offline and that position starts to go against you. But then you should be using stops really. I suppose you could use it over news as well if there is a possibiliy your original stop may be skipped. I dont see the point in normal trading conditions though.