And actually, cassp, the reason I use a big old expensive arranger is so I can use it any damn way I want

If a tune NEEDS LH bass (as this one demonstrates), I can do it. 76 keys is a BIG help when you use LH bass. If it needs full arranger, I can do it. If it needs SMFs and three splits, I can do it.

But to the main question of 'Why play LH bass on an arranger?', I guess you can break this into two parts.,. 'Why play LH bass?' and if you REALLY need an answer to that, you don't listen to a lot of bass players... The bass line is nearly as important as the melody, when it comes to making a tune memorable. It leads the chords (unlike arranger bass lines) and gives direction to the harmony, and acts as a powerful rhythmic element.

And 'Why on an arranger?' as if to say, 'why not on some OTHER type of keyboard?', well, if other keyboards were as flexible about their rhythm options, maybe I COULD use them for that (if not as an arranger), but as of now, even if you only use an arranger for drums and do EVERYTHING else yourself (as me and my guitarist do on much of our show), it still outperforms any drum machine made, with four Intros, four Endings, four patterns and seven fills all linked together. So, even if I weren't using arranger mode at all (but I do!), the arranger would STILL be the best choice of performance tool.

And they STILL don't make a drum machine with full Roland V-Drum Kits in them. The reason you spend MORE for a TOTL arranger is that is capable of doing MORE than any other keyboard (or combination of gear). Whether you use it ALL, all the time is up to you and your tastes...