Leaving clean dishes in your dishwasher overnight is perfectly fine. In fact, it's actually a good way to prevent your dishes from getting too wet if you're not able to unload them right away. Just make sure the dishwasher is turned off so that no new cycles start while you're sleeping. The trouble you may experience with leaving dishes in your dishwasher overnight is when they're dirty. Bacteria can start to grow, and odors can develop if you let dirty dishes sit too long. So, it's always best to run your dishwasher immediately when it gets full or run it before bed, even if it's not full yet.