What does this line of C/C++ preprocessor mean?

Question

This is Line 519 of WinNT.h (BUILD Version: 0091)

#define DECLARE_HANDLE(name) struct name##__{int unused;}; typedef struct name##__ *name

Why do we need a pointer to an struct with a single int member with a weird name called unused?

And will we ever need to use a line of code like this one?

HINSTANCE hInstance = new HINSTANCE__;

Overall declaring different data types with the same structures, doesn't make sense to me. What's the idea behind this?

DECLARE_HANDLE(HRGN);
DECLARE_HANDLE(HRSRC);
DECLARE_HANDLE(HSPRITE);
DECLARE_HANDLE(HLSURF);
DECLARE_HANDLE(HSTR);
DECLARE_HANDLE(HTASK);
DECLARE_HANDLE(HWINSTA);
DECLARE_HANDLE(HKL);

Answer 1

And will we ever need to use a line of code like this one?
HINSTANCE hInstance = new HINSTANCE__;

You usually use a HINSTANCE value returned by a Windows system call; I have never seen code executing a line like that.

Answer 2

The point is for the different handles to have different types so that, for example, a HINSTANCE isn't assignable to a HANDLE. If they were all defined as "void*", then there are classes of errors that the compiler could not detect.