It is tempting to move the saddle to adjust reach; it is cheap and easy. For general riding, saddle setback is a personal choice that comes from experience, but should not be used to adjust reach. However, reach will affect saddle position and saddle fit. The more intensely or long you ride, the more sensitive you will be to these variables.

Forward tends to correlate with easier transitions out of the saddle, more weight on the hands, more use of the knees, lower more aerodynamic position.
Rearward correlates with more use of the glutes, less weight on the hands, more on the sit bones, and a more seated style of riding. The handlebars also would be mounted closer, so you would be more crowded when standing.

There really isn't an optimal position. But if you experiment, you are likely to feel a preference. Just don't let the length of the stem dictate it.