I have tried to use my arranger with my 4-piece band (gt, sax, keys, singer) with moderate success. Since 90% of our music is midi-based, the rest of the band is pretty used to following the auto rhythm. I find that the biggest problem is matching the style to a song in a way that pleases all the band.

We have only a few songs I now use my arranger for. I have converted many arranger songs to midi to eliminate confusion.

To go back to the original question - any keyboard player playing with a live drummer and other musicians certainly doesn't need the arranger, but my PSR2000 has keyboard sounds that I love AND it is way lighter than my VR760. In that case, I just leave the accompinament off. But it sure is nice to have for those unexpected requests (the ones the rest of the band doesn't know.)