With the power of Interface-based design, Dependency Injection, and Inversion of Control containers; there's a propensity for the Extract Interface refactoring to be invoked on many classes in a code base and those classes used solely through the new extracted interface. This takes a giant leap towards loosely coupling, but can create new, unnecessary couplings.
Each class has its own interface that is used (hopefully) by one or more other classes. Each class may use that class in a very specific way, that is, it may not use its entire interface. By simply extracting an interface from a class and forcing all users of the class to be coupled to that one interface, you're forcing all those classes to be coupled to all of those usages. By providing one interface for all these client usages, it's suggesting one implementation (class) for the one interface. At the very least, each implementation must certainly implement the entire interface regardless of whether...