There's pretty strong evidence that the use of fire to cook food is what enabled modern humans, with their short (and relatively fragile) digestive systems and giant energy hungry brains to evolve. Cooking food makes more calories bio-available in food and also reduced the amount of energy the body needs to expend on that food to harvest calories... so there's more energy available for thinking (etc).
I had thought (perhaps wrongly) that our brains got a massive "boost" in capacity when our ancestors moved to coastal areas and the diet was dominated by (Omega 3 heavy) shellfish and crustaceans.
That’s a complicated question. The Wonderwerk Cave in South Africa where we found the first evidence of controlled fire also contained burned plant remains and bones, which could be interpreted as evidence of cooking. There were also burned fish remains found at the Gesher Benot Ya’aqov site in Israel, dated to about 780 kYA, which could also be interpreted as evidence of cooking.
By far the strongest evidence is the Qesem Cave in Israel, which had a central hearth and so many burned animal remains that it couldn’t have been accidental. Unfortunately the dating on that is controversial and the error bar is huge at 300 +- 100 kYA (200,000-400,000 years ago).
And cooking kills like 99+% of pathogens, which freed us from much of the parasite/disease stress other animals must live with.