SASS is an excellent tool, however, like with any tool, the output is only as good and solid as the coder applying it. I don't see any harm in it because the output is 100% in your control. Give that power to someone who hasn't a clue about CSS and the result can quickly become the same mess as we see when people who know nothing about JS use libraries.
With that said, I love SASS and use it on all my projects. I have my own little set of placeholders, mixins, and variables that I refactor over and over again which can be quite a time-saver.
As you said, the advantages can be plenty. One huge disadvantage, and that's a malady that isn't exclusive to SASS, is that everyone uses a different set of standards and practices. This adds unnecessary layers of problems when it comes to working on someone else's code. You don't just have the the issue of maintainability, flexibility, and best practices that may vary from your own in terms of CSS, but now you have to adjust your standards to match that of someone else's SASS as well. And when a third-party uses Compass or Bourbon with yet another set of additional layers, rules, and practices, then it can quickly become a very annoying experience...
I realize that people are currently proposing some kind of standards as a remedy. However, just like with CSS, I don't see how there can ever be a consensus on what is the "right way" to doing something, so I'm not positive that these efforts will go anywhere.