What role can advertising play in a shift in demand?

Positive or negative. Meaning it get make things better or worst or can actually start or stop a shift in demand.

A shift in demand will happen for many reasons (a question for itself) but advertising can be a vital part of shifting demand which can be driven by necessity or need.

Examples across the board:

Linux

Positive and with in the same company:

A company has office software that you used to have to install and it was Windows only. Now, the company is releasing a version for the internet which has many benefits for the company and the consumer. But the downside might be the loading and wait times on slower computers.

Advertising could come out to help push people to the new world by showing them the benefits of the new product.... sharing documents, watching live updates as others make them. The ability to open the document and view/edit/print on a mac, PC or Linux.

Positive and cross company:

A company is producing cell phones that are rugged. They want to show consumers that their products are great to use but also durable. Advertising could be launched showing various customers in their demographic that are in real world situations... using the phone and ultimately doing something such as dropping the product on the floor, in water, scratching against keys or in a car cup holder. The competing product breaks, gets water logged, scratches but the durable new product continues to be used as normal.

Negative internal company:

A company launches a new car. Typically their demographic was age 55+ but they want to try to break into the 25-35 market. The new products are designed and advertised for that market. While it's likely that some 25-35 people are now interested in the product, the advertising may alienate or ignore their current and faithful fan base. What is worse is that their 55+ demographic has a 80% liklihood to repurchase a second vehicle but that same figure is less than 30% for the younger crowd. Ultimately, the company may even had the same number of customers by name but selling far fewer cars.

Negative external company:

A company promotes a new device that is an all-in-one camera with video but in a rush or cost constraints they do not properly address all the features of the product while another company captures that well. Even though the companies product is better in every possible way, poor advertising and focusing on only part of the features allows an inferior product to take the market.