Winter's coming. It's already heating season. So how do you save money on heating costs? You've got to own your heat. Simple as that. You've paid for all that warm air already, so it doesn't make much sense to waste it now.
A simple enough premise - it's the application that gets complicated. We (and most building science experts) strongly recommend air sealing and insulation as high priority measures to make your home use less energy, make you more comfortable, and make the planet happy.