ISBNs – The Books All Have Them, But Why?

Is an ISBN necessary? By my research, absolutely not. At least, not if your publishing intentions are very limited. You can even publish on some ebook sites without an ISBN; however it limits your markets.
If you are just going to get a few hundred copies of your book printed to give to family and friends, or share them in ebook form through emails or on your blog, then the ISBN is unnecessary.
If you plan to publish through a publishing company or self-publish, in print or ebook, and sell your book, then you’ll probably need an ISBN.