Without a target, it’s easy to hold a profit “just a bit longer” until it melts away. With a target, the decision has already been made.
Example. You bought oil at $70, stop $68, target $74. The price reached $74, and the trade closed: +$4 per barrel. For a buy, the target goes above the entry; for a sell, below it. In the simulator, it’s the “Target” field; traders also call it take-profit.