Has anyone found a useful purpose for ion propulsion?
I've tried using an ion drive on the smallest possible probe, and the burn time for interplanetary travel was hours or days.
I can't imagine more engines would help much either due to their tiny thrust not outweighing the significant increase in mass which the required structural changes would cause.
I know about the solar glider, but there's not much purpose to exploring Kerbin, and normal jet fuel lasts a long time, so I don't really see that as a "useful" purpose.
Answer: Only use them if you are crazy hardcore or value fictional efficiency over your time.