This is considered to be one of the worst mistakes among book reviewers. This can make your reader easier to consider whether to read this or that book or not.
If you are assigned to write a book report or a book review, there are different ways for you to express your own impressions about a book and to demonstrate your attitude to it.
Remember that the more interesting your review or report is, the more your audience will be excited in finding this or that book.
Book reviews are more into expressing the reviewer’s own opinion about the book and often contain advice whether a reader should read it or not.
So, these are just a little bit different angles of the same view.