The Director is another piece of Trademinator. While the open source client does the trading, a single instance of the client only trades on a specific pair. The Director is as the name says, a director; it helps the open source client choosing what pairs to trade.
Although the use of the Director is optional, it helps you to automatically choose what pairs to evaluate. Therefore you can maximize the use of your computer resources better while instead evaluating a pair that will not likely present optimal trading conditions.