Brochures are a staple of any good suite of marketing collateral.
The physical feature that defines and distinguishes a brochure from a flyer is that a brochure is folded, and a flyer is not. But that is only where the differences start. Whether you need a flyer or a brochure for the marketing task at hand depends on what you're trying to achieve. To get quick bursts of information out about your promotion or event, a flyer is the way to go. But if you have more to communicate than you can fit on a flyer, or you want your customer to hold onto the information for later reference, a brochure fits the bill perfectly.