Windows Update Delivery Optimization was introduced with Windows 10 to make it quicker for end users to receive patches and other updates through Windows Update.
The concept behind Delivery optimization is a peer to peer network, either locally on your own network or across the Internet between other Windows 10 users and their devices, that speeds up the delivery of these updates by retrieving them from these other machines to shorten the distance between source and destination machines. Shorter distances means quicker downloads of the updates and patches.
By default on a new installation of Windows 10 Home or Professional Delivery Optimization is turned on however, you have control over keeping the option turned on or choosing to get updates just from machines on your local network or from other Windows 10 PCs on the Internet.
When many users hear about Delivery Optimization in Windows 10 their first concern is security, privacy and then followed by concerns about using up limited bandwidth to serve updates out to other Windows 10 devices across the Internet.
Microsoft addresses the first two concerns, security and privacy, in their Windows Update Delivery Optimization FAQ:
What security measures are used in Delivery Optimization?
Delivery Optimization uses the same security measures as Windows Update and the Windows Store. Windows Update uses information obtained securely from Microsoft to validate the authenticity of files downloaded to your PC. Delivery Optimization also checks the authenticity of each part of an update or app that it downloads from other PCs before installing it.
Can Delivery Optimization access my personal files?
Delivery Optimization doesn’t access your personal files or folders or change any files on your PC.
As for the last concern, using up your Internet data allowance sharing updates out to other PCs across the Internet, you can turn that option off as shown below and just share updates across your own local network. In fact, that last option should result in some overall bandwidth savings as updates are delivered to other machines on your local network.
So to adjust these settings start by opening the Windows Settings app and going to the Update & security settings page.
Select Advanced options to continue.
Next select Choose how updates are delivered.
This is the main Delivery Optimization page in Windows 10.
1 - This is the master switch for Delivery Optimization. Just toggle it On or Off as you desire.
2 - This option will only share updates to and from Windows 10 devices on your local network.
3 - This option will share updates between your local machines and Windows 10 devices on the Internet.
As you can see this is a safe and secure process but ultimately, like many other options in Windows 10, you have control over your devices participation in the process.