What are the downsides of robot vacuums?

A human cleaner has a really big advantage over a vacuum: it can move things out of the way. That doesn't seem like a huge problem, but the vast majority of robot vacuums lack arms. It can't just move a chair or get a hoover nozzle into a tight spot to clean up dust. There's also the unknowns to think about that it won't have mapped on its route, like toys, charging cables left trailing across the floor or even pet messes that can be spread around the house. That's not to say that robot vacuums can't overcome some of the issues.