You'll get a better buy shopping off season. Or maybe you're looking for a new car. Fall is the time to shop. Once vacation season is over there are fewer people car shopping. That means less demand.
Dealers have brand new models and last year's leftovers still on the lot.
That's more supply. The buyer should have an easier time. Let's move to the seller's side for an example. Suppose you want to sell your three bedroom home. The most likely buyer will have children.