Magnolia provides an app called Marketing Tag Manager out of the box, enabling content authors to quickly insert marketing tags across a website without the help of a developer. Tags typically collect analytics information or integrate with marketing automation tools. However, there are some special use cases like creating a QR code for the preview of pages on a mobile device.
 Read the blog article here:
https://www.magnolia-cms.com/blog/multichannel-preview-in-magnolia.html