Many breads and pastries require a high humidity environment for optimal yeast action and product baking. That led to the development of special ovens with enhanced humidity control for the "proofing" stage in baking. These ovens can also be used to hold cooked food for extended periods of time.
Most holding ovens surround food with hot air to keep it warm, causing moisture to evaporate. This shrinks food, makes it look less desirable, and also deteriorates flavors, texture, and consistency. However, food will not release moisture if the air around it is already saturated, so food in a proofing oven does not dry out.
These proofing ovens have been perfected to the point that they can keep some foods moist and others crisp in the same oven enclosure.