I sometimes wonder if I write too many book reviews, especially academic ones. I write about two a year, so that does not seem a lot. But they are a lot of work. After all, you have to read several hundred pages of often dense academic prose to produce a review of about 1,000 words. And then they don’t count for anything. If you’re in UK academia, they’re not REFable, that is they don’t count as a “research output” that will gain you brownie points in the big dreaded periodic evaluation of academic research.
Unless you’re writing for a commercial publication, you usually don’t get paid either. And if you’re unlucky, you might not even get a hard copy of the book you’re reviewing any more as publishers have become increasinly stingy. So why do it at all?

First, because you like it. I’m a very opinionated person. So any opportunity to give my opinion on anything is enjoyable. Knowing that people are sufficiently interested in what I think about a book is also a little confidence booster. So is getting published – even if it is “only” a review.
So secondly, It gives you a sense of achievement. You have worked, you have completed a task, and you have something to show for it. Unlike “proper” academic publications, which might require months or even years of research, this one is done quickly. If the journal you’re publishing in is efficient, the review will be in print within weeks. No other publication in an academic journal will ever appear so fast.
Staying on top of the literature
Thirdly, people actually read book reviews. They help your colleagues to find out whether or not a new book on the market might be useful for their research. So you’re doing them a favour.
Fourthly, you also help the author to spread the word about their book. Whether you liked the book or not doesn’t matter. You have drawn attention to the fact that it exists, and your colleagues might want to follow up on it to see if they agree or disagree with your judgement. If you’re lucky, you might start a conversation about a new and important book you want people to read.
And finally, writing reviews helps you to stay on top of the literature in your field. There is nothing that makes you read as quickly as an upcoming deadline. So if you’ve seen a new book you need to read, offer to review it!
gm