Windows Ressource files exist at least since Windows 3.x
> Don't have to bother with non unicode stuff
Just use the WinAPI functions that are prefixed with W (Unicode) instead of A (ANSI), e.g. CreateWindowExW instead of CreateWindowExA.
> Have access to well behaved widgets
Call CreateWindowEx (https://msdn.microsoft.com/en-us/library/windows/desktop/ms6...) (yes, the name is confusing, accepted) with lpClassName value, say, of BUTTON, COMBOBOX, EDIT, LISTBOX, MDICLIENT, SCROLLBAR (for a more complete list look at the MSDN site that I linked). This creates such a widget.
Think the UI the way I code it (declarative)
Don't have to think about screen resolution, colour depth,...
Don't have to bother with non unicode stuff
Have access to well behaved widgets
Can have portability if I need that
Even if I can't control 100% of the rendering process, my productivity has increased...