What are the things one should consider, as a postdoc, before accepting or rejecting an invitation to contribute a book chapter? The proposed book is a handbook in a developing field of engineering.
When I get an invitation to contribute a book chapter (or conference paper in an invited session), I usually ask myself the following questions:
Ideally, you should be able to answer at least questions 1 and 2 with "yes" before accepting the invitation. If your answer to question 2 would be "no", it may still be wise to accept the invitation in view of question 3. For this type of invitations, I would try to find a smaller contribution which fits the visibility of the proposed publication venue. In a book chapter, for example a summarizing synthesis of some of your previous results might be appropriate.
It almost certainly won't earn you any money.
It probably won't be read by many people. It will be cited by even fewer.
The collaboration may lead to future projects together.
It may involve a lot of work.
You might enjoy the process. Or hate it.
It may or may not help your career progression, depending on your field, your career to date, and the posts you apply to. If it's a book that will become a standard for one or more taught courses, your contribution may be crucial for your future teaching career.
In this particular case, when the putative author is a rising young authority in an engineering field, it's a rapidly-developing field that's attracting significant international interest, and many universities are introducing new courses in the area, then, (depending on the publisher, the other authors, and the other chapters) there's potential for the book to have quite a significant audience, so contributing to the book chapter would be attractive.
I would like to add the following: