The two speeds settings are as noted above for roll film and for sheets (film paper).
Jobo recommended a slower rotation speed for sheets or prints for larger machines, and had the two speeds on the CPE2. You can use the slower speed for pre heat or prep time, but you should use the higher speed when processing film.
There a long APUG thread about varying results with the different speeds when processing 4X5. In our experience in the field, the slower speed actually lends to better results when processing sheet film, but has no noticeable benefit when running roll film, other then less agitation, and therefor slightly longer dev times, but that is only relevant when processing color or e-6, and perhaps also super short BW runs.