Why it's not always a good idea to use stoploss :
It's not uncommon to hear traders give you a target price, stoploss and entering price. Do you wonder how they arrive at those random numbers ?
An individual trader is just a small fish in the sea. There are many large players trading every day - from market makers to institutional investors to algo trading and HFT firms.
Based on the day's stock price pattern, often market makers spot the level at which maximum tarders would have put their stoploss and then drive prices through to that level so their stop losses are hit before driving it higher (because they buy large stakes for big investors). You may have noticed that price often falls significantly before going very high.
For example, when Dolly Khanna bought a high stake in Deepak Spinners in June, the price went through the roof. But if you look at the price pattern, Deepak Spinners was trading at around Rs. 189. Price rapidly fell down to Rs 167 within a couple of minutes. Then at this price Dolly khanna bought the high stake (supposedly through a market maker) and the price then went upto Rs 215 within few minutes hitting upper circuit.
Now imagine if you had stoploss in place when this trade happened. I had invested in Deepak Spinners at the time and I made a good profit because there was no stoploss to stop me out.