Cooking food isn't necessary, but there are distinct advantages to doing so, namely, it improves digestion. This may not seem like a big thing but it ends up significantly increasing the amount of calories one can absorb, massively expands the types of food one can eat, and greatly decreases the amount of effort one has to spend to process those foods.
Comparisons to other primates are illustrative: non-humans basically spend most of their life acquiring food, chewing it, and digesting it, at something like 85% of their entire waking lives. Cooking reduces that to roughly 10%, freeing up evolution to take advantage of that calorie and time surplus by, say, growing larger brains. In fact, studies of chimps suggest that almost their entire social structure is built around the tradeoff between eating, calories, and digestion---even a small change in habit (say, by doing something other than eating with a mere hour per day) significantly reduces calorie intake to a net deficit. Without cooking there is literally no time to do much else.
In fact, the most scientifically dependable and reproducible form of dieting is just to eat raw food.
It is becoming common now among anthropologists to hold the view that cooking food has had the single greatest impact on human evolution, even over hunter/gather, agriculture, meat, or any of the traditional attributed causes. We would literally not be human if it were not for cooked food.