Summary
When you enable access to the Content Delivery Network (CDN), users will be able to connect to CDN online, access Skype Meetings App, and will use the simplified meeting join experience. From the July 2018 cumulative update 6.0.9319.534 for Skype for Business Server 2015, Core Components, this option will be enabled by default. If you have to revert the change for any reason, you can always do so by running the following cmdlet:
Set-CsWebServiceConfiguration -Identity Global -MeetingUxUseCDN $False