Yes, another self-publishing tool from Amazon. Before we move into the pros and cons though, let's get a definition of what KDP Select is. Paraphrasing from Amazon's FAQs page for the program, Kindle Direct Publishing is one of the options Amazon offers authors for self-publishing their digital content and earning more money.

When Kindle Direct Publishing is a good idea.

• When you want to earn money by having your book available to Amazon Prime members in the Kindle Owners' Lending Library. Members may read one book per month from the library, and you earn royalties each time your book is read.
• When you want to earn money by having your book available to Kindle Unlimited members in the United States. Customers pay a monthly subscription fee to read as many books as they like without being Amazon Prime members.
• When you want the opportunity to earn up to 70% royalties on your book.
• When you want to have access to several promotional tools, including Free Book Promotion - where you may offer your book for free for five (5) days, and Kindle Countdown Days - where you may apply time-sensitive discounts while earning royalties.
• When you are a new author and want the potential to dramatically increase the size of your audience.

When KDP Select is a bad idea.

• When you are not able to agree to Amazon's 90-day exclusivity clause. This clause remains in effect even if you decide to end your listing early. You are committing to allowing Amazon exclusive use of your digital content for 90 days
• When you have an established readership who would be upset by being limited to purchasing your book through Amazon only.
• When you want to offer your book for free, as an incentive, or at a discounted rate on your own website.
• When you have only authored one book. By offering your book for free on select days, you are also giving readers the opportunity to purchase some of your other titles. This is particularly useful if you have a series or sequels. Otherwise, you are basically giving your book to people who might otherwise purchase it.

Thanks to sites like Amazon and those that are springing-up as a result of Amazon's offerings, authors of digital books have more options than ever for publishing their work. Be sure to do plenty of research and weigh all of your options carefully before committing yourself to any one program of publication. Amazon loves to include that word 'exclusive', so if you want to offer your work in more than one place, you'll want to look elsewhere.