Q. Why do I need to put a hold on an ebook or e-audiobook?

The digital licensing for most of the downloadable ebooks and audiobooks follows the one-user-at-a-time-per-licensed-copy model, following the model of physical items. There's an interesting legal history behind why this is so; the extra technology involved in making sure that each use of a digital item is a permitted use is why there are so many steps involved in getting yourself set up to use these digital items.

Here's how OverDrive explains it.