If a “My book” is not in use, and is unplugged, will it loose its saved data?
Simple answer is “I hope not.” Better answer is NO. You can shut down your computer and you still will not lose anything. That’s why we use these drives!
BUT be sure you “Eject” the drive before you pull the plug. You Eject by selecting the drive with Windows 'File Locator" and right clicking on the name. A list will include "“Eject” option if save to remove. If no “Eject” it is NOT safe to remove it. Wait.