If you're like me and came here looking for a way to make sass --watch work with compass, the answer is to use Compass' version of watch, simply:
compass watch
If you're on a Mac and don't yet have the gem installed, you might run into errors when you try to install the Compass gem, due to permission problems that arise on OSX versions later than 10.11. Install ruby with Homebrew to get around this. See this answer for how to do that.
Alternatively you could just use CodeKit, but if you're stubborn like me and want to use Sublime Text and command line, this is the route to go.