I have never bothered with stop losses to my cost though just wanted to know if you set a stop loss and then when market re-opens and the share price is then below your stop is it automatically triggered ? Can market makers really drop a share price by say 20% to mop up cheap shares ? If you set a stop loss to lock in gains is it guaranteed to trade on drop ? or on rise ?
I'd say it depends on the type of share as well. If you're trading highly volatile or illiquid micro-caps for example, then you can easily be stopped out simply if the spread changes. I think the thing about market makers dropping prices 20% though is a myth.
If share price opens below where you set your stop, then you will probably get stopped out at that lower price. With some providers however, you can pay for guaranteed stops.
Generally speaking, using stops has saved me more money than it's cost me. Worth remembering though, that getting stopped out of a trade doesn't mean you shouldn't get back in again.
Someone needs to be prepared to take the trade on the other side. You can set your stop loss order but if no-one wants to take the other side ... If you have a large position,might be worth thinking about splitting it into several smaller stop loss orders.