Reason to Pass a Pointer by Reference in C++?

You would want to pass a pointer by reference if you have a need to modify the pointer rather than the object that the pointer is pointing to.

This is similar to why double pointers are used; using a reference to a pointer is slightly safer than using pointers.

50% of C++ programmers like to set their pointers to null after a delete:

template<typename T>    
void moronic_delete(T*& p)
{
    delete p;
    p = nullptr;
}

Without the reference, you would only be changing a local copy of the pointer, not affecting the caller.