The extra screen space obviously helps with Cubasis, but one of the handy things I just found was that using the Apple Pencil gives you a much greater degree of accuracy. Useful with effects where it is much easier to draw curves. I have not had a chance to see how useful the pencil can be with Cubasis but I am guessing that for editing the piano roll etc has got to be a much simpler task.
The Apple Pencil can be easily used in all apps and works similar to a single finger tap.
At lower zoom rates the pen allows more precision when working in the MIDI editor.
We think it depends on personal taste to use it instead of fingers.