I use the sequencer on my pa80 because I find it is easier to create a midi sequence with the internal sequencer.
Then I use the computer sequencer (cubase) to edit the midi sequence. This is generaly to edit extra notes, to modify the bass line, to quantize well. These operations seem more easy in the computer because of the large screen view and the mouse.
Then, my midi file goes on the pa80 where I edit the final mix, the effects, the balance...