I just removed GraphLab in ankurdave/incubator-spark@732333d78e46ee23025d81ca9fbe6d1e13e9f253 and in the process I had to add this option to Pregel to make it equivalent in power to GraphLab. I think this is fine since we've already modified the Pregel abstraction in other ways, but I agree with your concern about documentation. I added an [explanation](https://github.com/ankurdave/incubator-spark/commit/732333d78e46ee23025d81ca9fbe6d1e13e9f253#diff-e399679417ffa6eeedf26a7630baca16R68) of the option to the Scaladoc.