In a non-fiction title, it is often important to get in and out of it once you have read it. If you have a book that you go back to years after you read it for information there is nothing as frustrating in trying to find where something is at. A good index can make that trip easy–a bad index can frustrate you and no index at all can be worse. But what many readers may not understand is that if the publisher and author take the time to create a good index, it can often lead to a much better book.
In publishing professional books, my editors would sometimes work on large complex projects that took months to oversee. Originally, my editors often had to slog through creating an index just when they were experiencing major burnout. Making a professional index requires great skill and we were taking our chances when we asked our editors to do it. Authors were generally worse. You might think you were clever have a contract that called for you author to produce an index, but often you have something that was subpar.
As our work load increased though acquisitions, we started going to outside indexers. I found a great one who never made mistakes and created exhaustive indexes with lots of techniques that helped readers understand the entire work though the index. The process of creating the index would also give us some ideas on some last minute changes to the book that could make it better. Burnout of editors was reduced, books getter better, and books became more valuable and easier to use.
If you have ever opened a new book and then found there was no index, or if you have opened a book and found an index that is basically light and airy (and useless) and wondered why it turned out that way–well there is one answer–cost. A good index can cost a lot of money. Today, there are lots of index creation software that can do the job, but the purists who are looking for the best use a person not artificial intelligence to create one. There are not many out there, but if you come across one, you will recognize it–it is a thing of beauty.