What are some advantages - for both the reviewer and the writer -- of peer reviews?

Answer 1

The writer gets some valuable input on ways to improve his/her paper from the perspective of another person. The reviewer can often spot problem areas that went unnoticed by the writer.

In evaluating the work of a peer, the reviewer gets insight as to what characteristics strengthen a paper, and what characteristics weaken a paper. The reviewer can put these insights to work when revising his/her own paper.