@stefan There are two cases where this is useful for me:
The first one is also shown in the article, which is establishing spacing between paragraphs and other elements which is relative to the line height. It's good typography to make it a multiple of the line height.
The second one is components. For instance, I have a checkbox component with custom styling, so I need to draw a box next to the label. The label has a line-height, and the box's position depends on that. Setting a fixed line-height to the checkbox would solve that problem, but then it would mess up the way it integrates into the page, because the line height I set may be different from the current line height. With the new line height unit, I can make these calculations actually use the active line height.
@volpeon@icy.wyvern.rip