If name in C++ is not fully qualified, e.g. std::cout, it can lead to an unintentional error, such as mentioned at https://en.cppreference.com/w/cpp/language/qualified_lookup. But using a fully qualified name for ::std namespace, e.q. ::std::cout, is very rare, as I have noticed.
I'm currently looking at C++ code that uses ::delete to delete a pointer. A meaningless example of this is:
I can't think of a case when using :: to specify a scope would result in any code being generated. Every other operator I can think of actually (at least conceptually) generates code, it 'does something'.