Peers, especially group members, can play a massive role in shaping the community and affect general behavior. They can influence the attitudes and behaviors of individual members, which will impact cultural and societal issues.
Some of the behaviors that peer groups can help to amend include drug use, violence, and the development and expression of prejudice. There have been cases where peer groups have been able to improve individuals' academic achievements as well.
On the other hand, peer groups might also impact individuals negatively. For example, an otherwise good student will see a drop in performance because of wanting to fit into a peer group. The student focuses too much on what they can do to fit in, and they lose who they are in the process.