Regardless of when you use it... always use it with an aerator chamber. You get way more of the medication into the lungs that way. It's counter-intuitive, since you're moving the dispenser 5 inches away from your mouth, but the aerator chamber allows all the medication to vaporize before it gets sucked into your lungs. If you're just sticking the inhaler into your mouth, 60+% of the medication will still be in liquid form when it hits your tongue / throat, and it will stick there and eventually get swallowed.
An ER doctor explained that to me last weekend.