Usecase and function "Window Width and Height Override" setting?

Godot Version

4.3

Question

Can someone in detail explain what “window width/height override” does? Just override the initial width and height? Or upscaling the initial width/height to the new setting, so that i can use the initial resolution? I´m a little bit confused about several different informations. I would make a 320x180 game. On start it will be a little bit upscaled (windowed mode) because it is to tiny on big displays.And at last fullscreen option of course.