What is a potential risk of not refrigerating leftovers promptly?

Not refrigerating leftovers promptly poses a significant risk because food can become contaminated and lead to foodborne illness. When food is left at room temperature for too long, it enters what is known as the "danger zone," a temperature range where bacteria can multiply rapidly. This rapid growth can produce toxins that may not be eliminated even if the food is subsequently cooked; thus, consuming such food can result in serious health risks.

While some might think that food losing flavor, spoiling faster, or becoming too dry are potential consequences of leaving food out, these factors do not pose the immediate health threat that foodborne illness does. The focus on food safety emphasizes the prevention of harmful bacteria growth as the primary concern when handling leftovers.