A Microsoft account is what you use to sign in to Microsoft services such as outlook.com (or Hotmail), Office, OneDrive, Skype, Xbox, Windows, and more. It makes your experiences on devices and services more personal and relevant to you.
Any device (ex: PC, phone, tablet, laptop, Xbox, etc…) that you signed in to with your Microsoft account will be associated with your Microsoft account, and listed under “Your devices” online until you remove the device.
You can sign in to your Microsoft account online to find your phone, get support, and get warranty info for your devices.
You would want to remove a device from your Microsoft account after you no longer have it anymore.
This tutorial will show you how to remove a Xbox One, Windows 8.1, Windows 10, or Windows 10 Mobile device from your Microsoft account.