Why is it important to define a destructor in a class?

Defining a destructor in a class is crucial primarily for preventing memory leaks. When you allocate resources, such as dynamic memory, file handles, or network sockets, within the class, it is the responsibility of the destructor to properly release or deallocate these resources when an object of the class is destroyed. This ensures that memory that is no longer needed is returned to the system, preventing the application from consuming an excessive amount of memory over time, which can lead to reduced performance or application crashes.

In scenarios where a class dynamically allocates memory using operators like "new" in C++, a destructor must be implemented to include a corresponding "delete" operation to free that memory when the object's lifetime ends. If a destructor is not defined, the default destructor will be invoked, which does not account for the release of dynamically allocated resources, resulting in memory leaks.

The other choices do not directly address the primary role of a destructor. For instance, class inheritance pertains to how classes relate to each other, and while a destructor can participate in inheritance hierarchies to ensure derived classes clean up resources properly, this is not its primary purpose. Similarly, while optimizing program performance can be a consequence of effective resource management, that is not the specific intent of a destructor.