I was also curious about that and read the FAQ located at http://peerguardian.methlabs.org/pg2_faq.html

"Q. What lists should I use?

A. The only list you need is P2P. Others may want to block spyware or ads, etc. For blocking ads, it is recommended that you use something more tailored for that like the Firefox plugin Adblock or Proxomitron."