I tie a number of fly patterns that have a peacock herl body, and often rib them with my tying thread as a reinforcement. Many times, I tie the herl in nearest to the eye of the hook, wrap my thread back to the tail, then warp the herl back over itself toward the eye. Then I rib over the herl with my tying thread.

As you say, you can't see the ribbing (nor is it intended to be visible on those patterns), and the advantage is that it is quicker to tie in this manner than with a spearate piece of wire ribbing.

I don't do this, of course, on something like a Prince Nymph, where the ribbing is intended to be visible.