I left mine on years ago, it was a brand new machine. It decided to do a boil wash, and I mean boil, it melted the top of the machine and the soap drawer and ruined the bedding inside it, the problem was it did not switch off it was just stuck in wash mode and kept on washing and boiling. Really scary. I was really cross but managed to get it sorted out. So now I never leave the washing machine or dishwasher on when I am not in. Also stopped using the tumble drier as well. But thats another story.