My opinion; For my style playing and because I have been in love with the organ for many years, I like to have the left hand playing a sound that compliments the right. Trumpet in the right, saxes on the left � Saxes on the right � brass on the left � Flute on the right, guitar on the left.
My reasons for using a left hand sound;
1-One hand plays against the other, I can do more with a song, I have added another live sound. A sustained chord or a chord playing chords in the same manor as a guitar player would.
2-My left hand feeds my right hand. It sets up a path for my right hand. In reality both hands are working together. I find if I am not using my left hand my right hand can not improvise as well.
3-There�s the keyboard and then there�s my right and left hand. My right and left hands are the only real thing that�s going on � the keyboard does what it is programmed to do. Using a sound in both hands brings me closer to a live sound � less mechanical.
4-A big one for me � I have played pro guitar for most of my professional career, I loved backing a singer or a solo instrument, I added to their ability to perform. One great reason for me to use left hand sounds.
I set the volume for the left hand differently depending on the style of music, the volume is always just under my right hand.
IMHO, John C.