Research is one of the major responsibilities of a promotion agency. To develop a successful strategy, promotion agencies conduct research about a product, its target demographic and its image, before launching an ad campaign.
Full-service promotion agencies don't simply design full-fledged ad campaigns and then hand them over to businesses; they are also responsible for the nuts-and-bolts work of carrying them out.
It is the responsibility of the promotion agency to develop a research-based advertisement and promotion campaign. This means planning which demographic of the population to target, and how.
The basic function of a promotion agency is the development or exploitation of a brand -- what the website Bloomburg Businessweek calls the "personality" of a product.