I think the only real use for it is if you start to move the roof whilst at traffic lights etc, then need to pull away before the operation is completed, otherwise you'll pee everyone off sat still finishing the roof, or look a twat driving off with the roof stuck.
Also, its not really ideal, cos you've got to keep the button pressed, which is, in my opinion possibly dangerous, or at least inconvenient.
I dont get why it just stops if you go over the speed. Surely, if you go too fast, its going to act like an air brake. So, assuming the boot was in the upright position and you go over the limit, it will stop....in its most airbrake position! It would be better to decide to close etc if you go over the limit.
Obviously, if you have the smart top module then you dont have to keep pressing the button, so it is more convenient, but generally I think it best to avoid operating while moving if possible due to the risk of buckling the mechanism by hitting a pot hole etc. Plus, if you have the smart top module then you can open the roof whilst getting in the car, and close it whilst getting out---currently I have to wait for the roof to stop moving before opening the door etc....