I would never put an automatic stop loss for a share in a computer system. Far from offering protection, I believe it can be dangerous and takes away one's own control of the situation.
It is much more sensible to make a decision at the time based on what is happening.
Automatic stop losses may also lead to more downward volatility in relatively thinly traded stocks, or stocks at times where there may not be much buying depth with a number of automatic sells being triggered at lower and lower prices.
It also enables exploitation. Do you want to risk automatically being sold out of a stock because it has initially been deliberately knocked down on thin volume? With the seller sitting there at considerably lower levels ready to take yours and others' shares that are automatically stop lossed out?
