[hombre_fatal]

It's not for DRYing/golfing code.

The main use case of functions is that you can parameterize code. This lets you parameterize stylesheets, like set a base font size and primary color, and then derive your whole theme from it, from spacing to secondary border colors to how buttons look when they're hovered.

[gampleman]

You can do that with custom properties already. AFAICT functions don't introduce any new abilities on that front (apart from the aforementioned DRY-ing).