Trailing stop loss can be useful if you have a stock that has run up and you want to make sure you keep some of the gains. You can set a 10% trailing stop loss and then as the stock goes up, the sell order will adjust to 90% of the stock prices as it increases. The sell price only moves in one direction, up.
Then, if it drops 10%, the sell executes.
Be warned if the stock opens below the sell price on a given day, you may sell for less than your limit order.
The avuncular folks over at Investopedia have some more details on trailing stops.
Every investor's situation is different but, what ball percentage of your stock holds would you have a Trailing Stop Loss on? 10%, 20% more?