A sauce must be thickened enough to cling lightly to the food, this is called Nipper.   The preparation of high quality sauces requires experience and knowledge of how to properly handle and utilize thickening agents. The proper thickening and clarification of a sauce gives the sauce texture and allows it to stay on the palate long enough for the taster to experience all the nuances and layers of flavor. Although starches are the most commonly used thickening agents, there are others.