"I also think a comic, because of repeated images, can create an atmosphere of a place. There are certain things going on in the background that you don't have to mention over and over again. If you're writing about how much graffiti was on the wall in prose, you write it once, you don't write it every paragraph. Whereas in comics, it can be in the background on every panel so it sort of sinks into the reader's consciousness."
Here's a short but sweet interview with Joe Sacco conducted by Chris Mautner.