[tomtomtom777]

I think the most important drawback of the function for used once code is that its definition doesn't really map well to linear files.

There isn't really a proper place to put such function.

In this example, you would like to define add_vertical_scrollbar() right where it is used as this is the proper context where it makes sense to read it. But if you define it where it's used it no longer adds any clarity.