First, a simple interface minimizes the complexity that a module imposes on the rest of the system. Second, if a module is modified in a way that does not change its interface, then no other module will be affected by the modification.
Interfaces act as an important separation between the code implementation and how that code would be invoked by other systems. The interface should be as simple as possible, only requiring the minimum input. The goal is two-fold:
1) Hide compexity from the module user, and 2) Dettach the implementation as maximally as plossible from the interface to reduce the chance changes in the implementation will need to result in changes in the interface.
