Why is it important to know background information on book?

If you enjoy a book, then knowing the author can help you determine what other books that author may have written, so you can read them too. You could also perhaps contact the author to get an autograph.

If you are quoting text from a book, quoting the source (including the author) can help you avoid accusations of Plagarism, which is defined in the 1995 Random House Compact Unabridged Dictionary as: "use or close imitation of the language and thoughts of another author and the representation of them as one's own original work.".

Within academia, plagiarism by students, professors, or researchers is considered academic dishonesty or academic fraud and offenders are subject to academic censure, up to and including explusion.