Graphics are visual stimuli. It is placed and arranged in a certain way to portray a message that is legible or comprehendable to the reader. There are many way to execute this - from simply colour and shape composition to typography and illstration.
It is not an art however, it is merely done to put forward important statements so that they are not overseen. I see it more as a practice. This creates a massive area of interest as to WHAT is the key factor that will make graphical work stand out.
Advertising, like graphics, have the same goal. To put across a message and make it as consumer friendly as possible so that the consumer will engage in it. This is where advertising needs graphics to improve its visual qualities.
On one side of the coin, advertising is about words and emotions created by how they are used. This can affect people enough to feel the need for the product due to the way it is described. Graphics is essential in this case, as the study of type faces (typography) is a specialist job. Each type will help define a unique style, theme, emotion or aspect of the product.
On the other side, advertising is about how attractive the visuals are, for some poeple merely a glance at a good-looking product would be enough to buy it. There are endless amounts of graphic designers and illustrators in the industry now, each witht their own 'style' but it is up to the art director to select one accordingly to the way they work. Their choice may make the product look in a different league to others, or leave it invisible amongst all the other visual stimuli in life.
The graphic element of advertising, in my opinion, can either make or break the advert. Simply put, depending on how well the composition, colours, or content chosen creates a full idea, will make people see the product in a different light.