I agree you can write your Sass like that and 'do both', and I'm all for writing good Sass and building up higher level abstractions for re-use where you can.
However, there's no denying the reusability of classes like 'col-xs-4', despite the knee jerk hatred of that 'non-semantic' class from some in this thread, and I maintain that if all you needed was a col-xs-4 and your team know what col-xs-4 is, then why not just stick it in your HTML.
It doesn't make it less 'readable' for your team, and they're the primary audience.
> You can do either one without the other, but you should be doing both.
I guess I'm disagreeing you should always be doing both. Do both (create a new semantic class-name) where it makes sense. But when you already have a reusable class that does the job, and all of your team will understand, just use it.
The point is they are orthogonal issues. Creating re-usable chunks of CSS does not suddenly absolve you of the responsibility to make your HTML readable. You can do either one without the other, but you should be doing both.