Benefits of sales promotion:
(1) Spreads information
(2) Stimulates Demand
(3) Customer Satisfaction
(4) Stabilization of sales volume
(5) Create Product identity
(6) Performance Appraisal

Increase in Profit Levels:
Sales promotions enable companies to stand out in a competitive retail environment. This is done by creating on-shelf differentiation between their products and those of their competitors. Real product differentiation is quite hazy these days due to the convergence of technology.
Since the appeal of retailer products is to a huge extent determined by price, sales promotions enable companies to adjust the retail price of the product for short periods of time and with minimal price difference.
Influence Trade and Customer Behavior:

Price promotions, one of the functions of sales promotions, allow companies to change prices depending on supply and demand forces without changing permanent list prices. These changes in price enable companies to influence trade and customer behavior.
This is because price promotions enable companies to come up with strategies that would increase sales during the lean season. Price reductions during slow sales enable companies to attract more consumers to buy their products.
For instance, when foot and mouth disease became a problem, consumers refrained from buying pork products. As a way to attract more buyers to their products, companies reduced their prices to almost half of the original. Within days, sales had recovered.