Every massive galaxy today has a supermassive black hole in its center. Every massive galaxy was therefore at one time active. Active Galactic Nuclei (AGN) are a natural byproduct of normal galaxy formation. They're inseperable; you make a galaxy, you make an AGN. Quasars, in particular, are almost certainly tracing the high redshift formation of massive galaxies. If we can learn about Quasar environments, we will make important steps toward understanding galaxy formation...

(slightly paraphrased from astronomer, colleague, and friend, Fred Hamann, September 18, 2002)