There's a lot of threads on APUG and Flickr on this issue; as on most topics if you wait long enough to gather a big enough sample of replies, there will be an equal number of vociferous viewpoints at either extreme, and very few people sitting on the fence.
For what it's worth, when using my Jobo CPE2 with C41, I do prewash, for the simple reason that the instructions with the Digibase chemicals tell me too. Mind you, those instructions omit to mention the need for a rinse before and after fix, so they're not that good a source.
With b&w, I only prewash with TMax, to remove some of the stain.