The larger sensor simply allows for higher quality photo'sphotos. I assume the very low noise ratio will give a photo from a fullframe just a little more of a "professional" look.
The people using fullframe'sfullframes invest in their equipment because they spend a significant amount of time making photo'sphotos. Any professional will probably carry a fullframe. So naturally the collection of fullframe photo'sphotos out there is of much higher quality.
But is this statement still popular? Sensors have improved dramatically the past years. Large sensors where obviously better in the past, but now the small sensors are getting better. SoftwarecorrectionsSoftware corrections fix most of the problems these days. Micro-four four thirds are getting popular because most people don't even see the difference anymore.