I believe that ads increase the exposure to products, which in turn promotes sales. I believe the more any one product is exposed and communicated over the public the domain the larger the chance of it is to be purchased by consumers. I also believe that the more brute an add is, the more effective it is.
Advertising promotes sales significantly, which is why it is such big business. Consumers are exposed to hundreds of ads on a daily basis- some of which they are cognizant of and some which they hardly notice. The ones they are aware of - such as sales fliers for stores they may shop it - promote huge sales. Stores entice customers to visit through deep discount sales. The ones they are less aware of still promote sales as customers learn to associate retailers with what they sell so that when next they need to purchase that item the name comes to mind.