I play left hand bass on the keyboard all the time. And as UD points out, it really adds the LIVE touch and synchronization to the music. It adds that extra accents and punch a lot. I usually jack up the left hand volume the highest level along with drums and keep the main and layer voice lower.

I use the drum rythms only without the accompaniment. And I tell you, I am NOT missing a thing without those other stuff going on. My right hand does the comping with pianos, layered strings and occassionaly throw in solid guitar voice, brass, sax, whatever to spice things up.

Everything is TIGHT !!!