Virtual inheritance is a C++ technique used to address the "diamond problem" in multiple inheritance scenarios. This problem arises when a class inherits from two classes, both of which have a common base class. Without virtual inheritance, the derived class would contain two separate copies of the base class's members, leading to ambiguity. By using virtual inheritance, such as class B : public virtual A, the derived class D that inherits from both B and C will only have a single instance of the base class A. This ensures a unified copy of A's members is accessible. However, virtual inheritance only has an effect when there are further derived classes that would encounter the ambiguity. A co-worker of Mandy has been overusing virtual inheritance, applying it even when it's unnecessary. For example, marking a final class SomeSpecificDerivedClass with public virtual SomeBaseClass has no practical benefit. A final class cannot be inherited from, rendering the virtual inheritance declaration redundant. Therefore, defaulting to virtual inheritance in all situations, as Mandy's co-worker does, is often an inefficient and unnecessary practice.