Originally Posted by haz

No, I didn't read that from weight watchers. No, I don't mean that cardio 5 times a week is useless. No, I don't mean that diet helps you keep or build mass.

I mean that danieljamie wants to lose weight, and that given the same amount of time and effort diet gets you results faster than exercise, so he better focus on that. A tough workout for unused people burns 600 kcal and takes 1-2 hours. With diet you can cut 1200 and save 1 hour of cooking.
Additionally, people often eat snacks and energy supplements after workouts for the "feel good" factor, which kills 50% of the set.

As to calories deficit, it's physics: a kilogram of fat is 7-8000 kcal, and your body works out of energy. You don't kick in enough, it will burn it from fat.

Bottom line: if you want to lose weight, diet is just simpler, faster and more trackable than exercise. If you have time and brains to implement well both, then welcome.