When 758 built-in sounds just isn't enough. I don't know how many sounds my Roland RD700 has, I usually play the default piano that comes up when it turns on. The Tone Wheel organ lets you use the four sliders as drawbars with a switch to choose which bank. I have a Hammond tone wheel generator waiting for a project. A friend inherited an organ when he bought a house and said he'd either give it to me, or throw it away. I let him throw it away, but I kept it's heart.