My workflow usually involves laying down a guide track using the arranger, for which I am VERY grateful there is a built-in sequencer in the G70 (I never said they had NO use!). I then transfer the SMF by USB back to the computer and open it in Cubase.
I then start muting each arranger track, and replacing it wholesale with my playing, which gets rid of the 2-4 bar 'snippet' sound of arrangers, and perform a REAL bass line, with voice leading and walks that go where the chord structure goes (probably the biggest weakness of arrangers is the bassline never knows what the NEXT chord is until you get to it, so leading and walking are close to impossible).
A bit of editing to the drum track (I'll often leave that intact if the feel is right, but I'll change the fills up so none completely repeat, and add in any stops or breaks that the arranger couldn't manage), and it's mostly done.
If it's intended for performance solely on the G70, I'll then transfer back to the arranger, and do some fine-tuning to the drumkit (changing snare and toms pitch, panning), and some some basic voice editing in the Makeup Tools (easier there than dealing with the sys-ex from the computer!) and a final Save.
If you are content with the song as performed by the arranger alone, then the computer is not a necessity, and for the 'I got to have a sequencer for when the moment strikes', I say that I never HAVE said I don't want or need a sequencer onboard AS WELL as a computer at home, they are very handy for capturing inspiration (or the lack thereof!) wherever you are.
But unless you do the bare minimum of editing, rearranging, deconstruction or wholesale reconstruction, a computer makes a FAR better tool than even the best onboard sequencers. As I said earlier, you CAN surf the internet on a cell phone... but if you had a computer, you would probable prefer to do it that way...
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An arranger is just a tool. What matters is what you build with it..!