Here is my 2p regarding longer term trades.
I believe that some general patterns exist within the markets (even if just based on high probability). These patterns are not absolute but relative to the current price levels, so there is a continuous adjustment. What I'm aiming to do is to position myself so that my profitable planned exit price is kept within the pattern. This might mean adding to losses, too. For example: buy @ 7500 with target of 7550. Once the pattern is adjusted and target moves down (can be several days later), e.g. to 7470, I will buy more at a price that would give me profit @ 7470. Sooner or later, target is hit - patience is key here. In such systems stop loss in itself can be very inefficient as it severely limits profits.
I do some scalping as well, only if I'm not too busy at work. Here, experience tells me that stop losses are needed and helpful.
What works for me might not work for you, though !