Protein does three things no other macronutrient does as well. It's the most satiating — gram for gram it keeps you fuller than carbs or fat, so higher-protein diets tend to reduce calorie intake without conscious effort. It has the highest thermic effect, meaning roughly 20–30% of its calories are burned just digesting it, versus about 5–10% for carbs and 0–3% for fat. And it's the raw material for maintaining muscle — critical when you're losing weight, because weight lost as muscle rather than fat leaves you weaker and lowers your resting energy burn.
Practical target: research on body composition supports roughly 1.6 g per kg of bodyweight per day for people who train, with benefits plateauing beyond about 2.2 g/kg. Most sedentary people eat well under this. Spreading it across meals rather than one large dose is generally better for muscle protein synthesis, and there's no evidence that high protein damages kidneys in people with healthy kidney function.