"Some 60% of American Marketing Association member marketers say halting or reducing spending on key marketing programs is the biggest mistake marketers can make in an economic downturn, according to(pdf) a recent AMA survey."

In a downturn, marketing becomes even more important to the company's bottom line, making a profit. A marketing plan is key to establishing the dimensions of your market, where you fit according to your product and identifying where a company should focus its marketing budget to achieve the best overall results.

In a downturn, marketing helps to identify new markets, target new customers and determine the value of the product.  If the product that is currently in production does not have a sustantial customer base of support, if sales are slipping and competition is securing your former market share.  Marketing helps to identify the need for a product revitalization or reinvention. 

"In a challenging economy, you must find new ways to make marketing work more effectively, get more out of marketing investments, and measure and account for marketing decisions. In short, you must make changes. Doing the same things in an uncertain economic environment and expecting the same results is, at worst, a definition of marketing insanity. At best it is a flawed strategy."

Check out some of the major marketing campaigns at the link below.

http://www.enotes.com/marketing-campaign.