Windows 10 for desktop users shipped with both the new Microsoft Edge web browser and the older Internet Explorer 11, primarily for business and enterprise customers who needed to keep using IE11 to run older web apps. Now Microsoft is allowing those customers to set up Microsoft Edge so that when it encounters a legacy site, it can automatically open in IE11.
"IT Pros can use their existing IE11 Enterprise Mode Site List or they can create a new one specifically for Microsoft Edge. By keeping Microsoft Edge as the default browser in Windows 10 and only opening legacy line of business sites in IE11 when necessary, you can help keep newer development projects on track, using the latest web standards on Microsoft Edge. For customers that have significant legacy content, we are also providing the ability to configure any Intranet site to open in IE11 when a user browses to it using Microsoft Edge. This functionality is available as part of Windows 10 and has no additional installation requirements."
Again, this feature is mostly for business users of Windows 10 and is not needed for most consumers using the operating system.