The only thing I can think of that really matters which can’t be solved by just wrapping the data in an inner heap allocation (like std::vector) is with the pointer to the vtable for virtual function calls.

If anything, I’ve found it’s more useful when I want to bypass such wrapping to force a class to use some particular memory (like from a bulk allocation). The STL is pretty good, but there are warts that which still force the default heap allocator like std::function.