Steady levels of insulin make it much easier to maintain a caloric deficit. If your blood sugar is yo-yoing all over the place, you're going to get cravings, increase your risk of bingeing, etc.
While it's easy to fall back on 'calories in, calories out', weight loss has much more to do with psychology, physiology and compliance than physics.
edit: Here's a nice review article from Nature, which tells you all you need to know: http://141.213.232.243/bitstream/2027.42/62568/1/414799a.pdf
It starts:
Despite periods of feeding and fasting, plasma
glucose remains in a narrow range between 4
and 7 mM in normal individuals.