I always have a S/L, as previously metioned its for risk/cash management and also a way of telling you that your analysis or strategy was wrong this time.
There will be times when you lose or have losing streaks, its normal, and by having stop loss in place protects you.
Remember to take a loss and let your winners run. Once my winner is running, what I like to do is close half the position and bring the stop loss of that position to break even and leave the trade running. That way my trade has already earnt me money(winner) and if it then goes against me it will hit the stop at break even.