With TOTAL automaton, the greatest issue would be that nobody would be working, and the rich would own all the production capacity, so nobody else will earn any money to buy from them. Effectively, overall demand would dry up even as people are desperate for the things they need, but can't afford to buy even at lower and lower prices. Even the wealthy would lose out, because there would be no consumers left able to buy their stuff. Essentially, the economy would grind to a halt unless wealth redistribution was forced by socialism, so that more people could afford to buy things.
To some extent we are already starting to see a shift in this direction, with increasing automation, ever more skewed wealth distribution, and slowing growth and demand as the masses can't afford to buy what they need, even though it can be produced more easily. The picture won't pretty if nobody can earn a living without any income.
However, that is only the case with complete automation, where there is literally nothing left for people to do. In practice, simple repetitive tasks tend to get automated first, leaving people with more time to perform more complex tasks that cannot (yet) be automated, and so overall productivity and efficiency increases without impacting overall employment. So people are still earning a living wage, and they can buy more things that are now cheaper and easier to make.
Automation really only becomes a problem when even the most complex tasks can be automated, and that is the great risk of artificial intelligence that people like Stephen Hawking say will spell the end of the world. In my view he's probably right. Not because machines will consciously take over the world, but because they will make people and employment (the potential to earn a living) redundant.