Leaving roasted potatoes out overnight at room temperature can be risky. Bacteria, particularly Clostridium botulinum, can grow in cooked potatoes left at room temperature. This can lead to foodborne illnesses. Even though they may look and smell fine, it's best to err on the side of caution and avoid eating them.

If the potatoes were kept above 140°F (60°C) in a warm oven, they may still be safe, but if they were left to cool down, it's safest to discard them.