to using ball-bearing (or other low-friction) batten-cars: The advantage is that you can reef while running downwind. Otherwise wind pressure prevents it on a higher friction setup, and you have to round up to reef.

(added edit) This advantage can help avoid a knockdown as the difference in apparent wind (from running) when you round up can easily exceed 10 or 15 knots -- very significant if you're already overpowered on the run.