Did you know that 70% of your metabolic rate is determined by your lean body mass? 'Lean body mass' includes your organs, blood, and MUSCLE. What is your 'metabolic rate'? It's how many calories your body needs to function at rest.
Muscle burns 6-7 calories an hour at rest per pound of muscle whereas fat burns only 1-3 calories. Muscle also weighs more than fat because it is more dense, but it takes up less space in the body making you smaller but not necessarily lighter.
Do you want the freedom to eat out once and a while? Eat that piece of chocolate and not fear that it's going straight to your ass? Not starve yourself after you overate pizza the night before and do 2 hours of cardio to try to burn it off? Well the more muscle you have, the more you can 'get away with'. Those calories will be better utilized by the body if you have a higher percent of muscle. Somebody who is 25% body fat may only be able to eat 1600 calories per day before they start to store the rest as fat whereas someone who is 19% body fat may be able to eat 2200 calories per day. I know which person I'd rather be!
Can you see how that would be easier to lose extra body fat or maintain your physique if your body needed more calories? You could lose body fat eating 2000 calories instead of eating 1200 calories, feeling starved and then hitting a plateau because you can't decrease your calories any more.
Muscle is more metabolically active. It purely needs more energy (calories) to survive. So if you want to have balance in your diet, you need to start lifting those weights!