After a brief introduction, this contribution will discuss practical strategies to exploit the unique science potential of closure phases in optical interferometry, especially in the case of only three telescopes when direct imaging is near-impossible. Prototype source morphologies will be investigated in detail (binary and "dust shell + star"), and will illustrate how closure phase measurements can be used both for "Precision Interferometry" as well as qualitatively new probes of circumstellar environments. During this meeting, the notion of a "Closure Differential Phase" came to light, and some interesting properties of this quantity are here introduced.