Pros and cons of writing a book review?
There are several benefits of writing book reviews for publication:
- Develop an understanding of the publications that are out there. Just like how reading academic papers affords you the benefit of being abreast with the latest research, writing book reviews allows you the opportunity to learn more about a field.
- Develop a relationship with a journal. Journals need people to write book reviews. It can never hurt to build a relationship with a journal and its editors.
- Develop a profile in the academic community. Book reviews are in no way akin to writing an academic article on a research subject. But they can put your name out there and allow you opportunities to become better known to you academic community.
All told book reviews allow your voice to be heard on a subject.
Since Vladhagen only mentions pros, let me list cons also. They may or may not apply to you. Feel free to edit my answer to add more cons.
As you've noted, It takes away time from your research. Moreover, it can also take time away from other important things like preparing for teaching or preparing for meetings, talks etc. As some researchers feel the need (or the pressure!) to do the same amount of "real work" (i.e. research) every week regardless of what else they have to do, it could also take away free time and/or time you could spend with your partner, children, friends or hobbies. Especially if you procrastinate and do all the work in the last week. Don't underestimate the amount of work such a review is!
(I assume the review is public, not private.) Depending on the attitudes of the people in your field, you could step on someone's toes: If you write something, some people may not like what you have written, get angry and you could lose reputation with them. Of course, you can also make the authors themselves angry if you write something bad about the book or show some misunderstanding in the review.
If the book is controversial, so will your review be; you can probably not do anything right with the review. I heard about a math research book (in Model Theory, I think) where the author inserted in every chapter a (unrelated) pornographic/sexual picture. I wouldn't want to be a reviewer of this book -- it's hard to do such a review right, especially if the author is much more well-known than you. For a popular science book, scientists often argue about whether a book is "too scientific written" or "too less scientific written".
It can be hard and dull to read a book carefully for a long time, especially if the author does not write too well.
Readers who buy/read the book because of your review **may get angry if they don't share your opinion. So many times I wanted to learn from books where the reviews said they were "didactically well written" only to find out that the reviewer had no idea about didactics and the book was not didactic at all.
You may lack the knowledge about (some of) the topics the authors write about.
- People may look at your CV and think of you as unproductive because you "wasted" your time with this review. Unfortunately, those people exist -- on this site, there are even stories about hiring people who see good teaching evaluations as negative! Of course, one could say "those people are stupid, I don't want to work for them anyway" -- in reality, in academia one often does not have so many choices (especially if you are not geographically flexible).
- You are make a commitment to complete the review. While most people are hopefully understandable, some people might not like it if you cannot finish your review because of something more important to you which might come up (new position, new partner, new children, sickness). Most likely, reneging is worse than not accepting to do the review.
Of course, some of those points may not apply to you but I found it important to list them all anyway.
One small advantage is that you get a copy of the book "for free" (admittedly not really worth it in terms of the time you'd put into writing the review) ... This is more of an advantage for expensive technical books that you'd like to own.