Stop limit orders are a good way to determine when to sell, which is the toughest decision to make. Even if you are dollar cost averaging into a position, you can set a limit order to protect profits, or prevent a large loss. I've seen some recommendations to put a stop limit order of a certain percentage on any new position for stocks/ETFs as a way to keep emotion out of your decision. A trailing stop limit order allows you to sell only when a stock/ETF goes down.