To many graffiti may seem as just a destructive thing to property and whatever else is written on by them. But the main thing that I noticed awhile ago was that graffiti writers get much more notoriety and exposure then many advertisements.
Many graffiti writers ultimate goal is to basically have their work seen. If you look in the picture above you can see the white trucks have some of the same names and letters on them. Meaning that as these trucks go out and around various New York cities they will be seen by a large amount of people.
So when the next time your out around your town and you see graffiti just think of placement and location and also how many people will be able to see their work.