For the body. Yes, run a deficit. But some "calories" will work against weight loss even if in a deficit. Others will help take it off. Some fuels will take you farther than others, even if they contain the same calorie amount.
Me? 75lb down in under 5 months using a combined strict Ketosis (this primarily), with a Calorie Defecit, a fasting window, paying attention to the glycemic index of carbs I ate, and exercise. Now in maintenance mode for over the last year.