I mostly use Craft for syncing with Invision and the library to always have the last update for the colors and text styles of our style guide. It's really useful, and I can't complain except when it makes Sketch suddenly crash. At first, I thought this was a Sketch problem, but after looking into it, I learned that Craft could be sometimes instable. Still, it's worth the risk 😉
Am a recent convert to Sketch + Craft, and the connection to InVision raises productivity dramatically. Large files with lots of artboards/hotspots still face issues synching up, though, which is a bit annoying.