Writing reviews can help writers.
It is well known that good writers read widely. Other authors’ love of words and language stimulates creativity and the richness of vocabulary.
Writing reviews of books adds to the learning opportunities. The reviewer identifies what works and what does not. Ways to build tension, excitement, characters, scenes and credibility are revealed.
A writers' group advised that some reviewers share their reviews with the author of the particular work, with the intent of possible mutuality. My only attempt at this revealed that the author was extremely defensive against even the slightest criticism. My learning was that life is too short to seek reflected glory. Also, being averse to criticism blocks one's full potential.