Over any 24 hour period we are continually bombarded by visual information that we have to process and make decisions upon. Much of this information is instantly processed at an instinctive and emotional level, a level at which we are completely unconscious of.
Traditional research techniques rely upon self reporting methodologies, which are fine if you want to explore what people think they looked at, but if you really want to know what draws their attention the only way to do it is by using eye tracking.
Invest your time to look at the video below, it only lasts two and a half minutes but will prove beyond any doubt just why eye tracking is such a powerful tool in the researcher's armory.