Discuss the role of sales promotion

Discuss the role of sales promotion as an element of promotion mix.
or
Discuss in brief sales promotion with the help of a suitable example.

Sales promotion refers to short-term incentives, which are designed to encourage the buyers to make immediate purchase of a product or service. These include all promotional efforts other than advertising, personal selling and public relations, used by a company to boost its sales.
Sales promotion activities include offering cash discounts, sales contests, free gift offers and free sample distribution. Sales promotion is usually undertaken to supplement other promotional efforts such as advertising and personal selling, e.g. 20% off on branded clothes, free samples with new products, gold coin inside the bag of tea leaves, etc.