Apart from nesting, I think importing modules in SASS is more friendly towards big projects and teams.
Having one code base for minor changes, but having different modules for, say, the navbar, but inside the navbar we could have more modules for social icons, and one more menus, and one for the logo. And all that can be be imported on a bigger module called _navbar…
That ability is what makes most css frameworks’ magic work.
And of course, the computational factor of it. I called it math, but you were more specific.