A stop loss order is an order that closes out your trading position with the intent of cutting your losses when the market is moving against you. There is no rule of placing the stop loss order, it all depends of your trading strategy. Using stop loss order should be a part of any trading strategy, so your account is protected from the unpredictable markets movement.
I think, stop order is an order that place to exit a trade, especially when making loss. This stop order helps to minimize risk in the market so that the risk will be limited because since it is fluctuating market, there is every reason to set this order for we do not know the outcome the of market.
Placing limit profit and stop order is the soul of forex. That said, it will depend on your strategy to put stop order or not. From personal experience, stop orders are a pain (I dont use them) the fluctuation are so volatile that 80% of the time it will hit a medium range stop order before hitting your profit, it is far more productive to concentrate on better entry points.
The name shows that this stop loss used in any trading type as in limit order it saves traders from any unexpected loss. It limits loss to a specific point at which trader sets . When market comes to that position order is placed and trading is being done if it is in favour profit hits other wise he gets loss what he setted before.