What's the point of hot food?
I'm assuming you're asking why food is often served hot, not why food is often cooked.  Cooking can obviously have a major transformation on food.  While people often debate whether cold pizza is better than hot pizza, I haven't heard anyone arguing uncooked pizza is the best.

The main reason why foods are often served hot is because higher temperatures  increase our perception of taste.  However since this increase not uniform across different compounds it can also alter the balance of tastes increasing some more than others, possibly creating a better or worse overall flavour. Temperature can affect how the texture of foods is perceived and even the amount of pain felt when eating spicy hot foods. 

Probably the easiest way to test this yourself is would be to compare either soup or coffee served hot as normal and cooled down in a refrigerator. You should notice when served cold the soup has less flavour, and the coffee is noticeably less bitter.

Another thing to try would be beer.  It's hard not to notice the difference between an ice cold beer and a room temperature one.  While most people prefer their beer as cold as possible, the recommended temperature for craft and specialty beers is often somewhere in the cool range. That's so you actually taste the beer you spent more money on.