Ever notice that food tastes better when your spouse cooked it (controlling for talent of course)? Why do leftovers often taste better than when the food was fresh? I believe the same phenomenon explains both of these.
A large part of tasting is actually smelling. You can verify this by, for example, eating an onion with your nose plugged. Our sense of smell tends to filter out persistent smells after being exposed to them for awhile so that we cannot smell them anymore. This means that when you are cooking in the kitchen, surrounded by the aromas of your food, you are quickly de-sensitised to them. Then when you sit down to eat, it is like tasting without smelling.
When your spouse has done the cooking you were likely in another room, isolated from the aromas. When you walk into the kitchen to eat, you get to smell and taste the food at the same time. That’s why it tastes better to you. The same idea applies to leftovers. It takes much less time to reheat leftovers than it took to prepare the food in the first place so you retain sensitivity to more of the aromas when it comes time to eat.
I believe that when recipes direct you to “allow the food to rest so that the flavors can combine” what is really happening is that you are induced to leave the kitchen and return with a renewed sensitivity. This also explains why dinners which you spent all day preparing are often disappointments. And it implies that when you have guests over for dinner you should entertain them outside of the kitchen so that they will enjoy the food more when it is ready.