Advertising is about developing brand awareness, and showing consumers how products meet their needs. The most basic need that you can market is a functional need. When you show how a product fulfills a functional need, you are demonstrating that it fills a practical need in the consumer's life. This is fundamental strategy for primarily functional products, but even higher-end offerings have a functional purpose.
When you market food to fit the functional needs of consumers, rather than desire for food, you are focusing primarily on its nutritional value. A simple value proposition may be that the food provides a low number of calories, fulfilling a consumer's functional need to reduce caloric intake. You can go further, focusing on specific needs such as certain nutrients. For instance, you might advertise food as providing the minimum daily requirement for a certain vitamin or mineral.
Personal goods are well suited for marketing to functional needs, because many of them are designed primarily to fulfill basic needs, even when also offering style and flair. For instance, shampoos and soaps are marketed to show that they fulfill the function of cleaning the consumer's hair and body, no matter what other benefits, aesthetics or refinements they offer. Many types of clothing, such as work clothes and outdoor wear, can be marketed to show that is durable and serves functional purposes, such as comfort and keeping a consumer warm and dry.
A service can provide many benefits, but from a functional perspective, what matters is the basic purpose of the service. For instance, you might advertise a dry cleaner as being able to provide timely cleaning of suits and other clothing that cannot be washed at home, offering a 24-hour turnaround. If you provide an accounting service, you would advertise your ability to do taxes and prepare financial documents for individuals and businesses.
High-end goods are not typically marketed using functional needs alone. Even so, it is important to show that they still fulfill these basic needs. For instance, a luxury watch might be marketed as prestigious and appealing to emotions, but it should also be shown to be a precisely functioning timepiece that fulfills the consumers need to tell time. Similarly, a sports car might be marketed as fulfilling psychological needs, but the consumer will want to see that it fulfills his basic need of getting from point A to point B.