From The Free Forex Encyclopedia
While other trading styles emphasize the reading of signals based on mathematical formulas or price action patterns, or fundamental analysis alone, discretionary traders are the "jack of all trades" of the Forex market and tend to incorporate all forms of analysis. These traders not only rely on their well developed trading processes and framework of the fundamentals and technicals to make a decision, but also sometimes intuition as well (i.e., years of market experience). Because of their experience, discretionary traders tend to be flexible with their trading rules and more adaptable to market changes.
The downside to the discretionary trading style is that trading decisions are more susceptible to the strong emotional effects of managing financial risk. Also, depending on the time frame, it requires more attention to the market than mechanical or automated trading methods.