The Susy documentation says:
The only requirement is Sass, but Susy was built to be part of the Compass ecosystem, and we recommend pairing with tools like Breakpoint and Vertical Rhythms.
Of course if you want to use the recommended Vertical Rhythms, which is part of Compass, you're dependent on Compass.
But other than using the functions/mixins Compass provides, are there any reasons why I would want to use Compass with Susy? Are there parts of Susy that only work, or work better, when Compass is available?
For example, in the file _breakpoint-plugin.scss you see that Susy actively checks if the Breakpoint Plugin is available, and changes its behavior accordingly. I want to know if there are similar optional dependencies on Compass built in.
PS, In reaction to the close vote:
I do not mean to ask for opinions. I want to know if there are features in the Susy codebase that do not work (or not as well) when Compass is not available. I will update the title to make that more clear. Please let me know if you see more ways to improve the question.
Check the custom support docs for all our integrations. Basically: we'll use Compass prefixing, clearfix, vertical rhythms, and rem fallback if you ask for them.