The optimistic case is technological deflation. Where goods and services become so cheap, you don't need a lot of money to afford them. If you can have a robot sort packages like,
https://tech.yahoo.com/ai/articles/human-intern-beats-figure...
Why have a human do that? I don't think there's a person alive whose life goal is to sort packages. A human will lose a job, but only a job they accepted because the human needed money. Well if the package sorting drops the price of things, they don't need as much money. Now if every job is robotic, everything becomes cheaper to the point we don't need money for very many things at all.
That's the optimistic case.