The JPEGs mean you have mono shots for immediate use and also proof images that can help when you process the raws.
The third way, and the best of both worlds, is to set the camera to monochrome picture mode and shoot both JPEGs and raws in-camera. The JPEGs mean you have mono shots for immediate use and also proof images that can help when you process the raws. Essentially, this option is win-win with the only downside being the memory needed for shooting and storing two files of every image. This is the method I use although I only archive a few JPEGs.