In an Active Directory domain, we generally rely heavily on group policies. Microsoft best practices say that you should have at least two domain controllers. Most of our clients have two or more domain controllers. Those domain controllers need to replicate Active Directory information, DNS information, and Group Policy information (i.e. SYSVOL) so that everyone properly gets whatever you intend them to get.
Microsoft has made the recommendation that SYSVOL replication be migrated from File Replication Service (FRS) to the more reliable DFSR. Furthermore, Microsoft has stated that Microsoft Server 2016 is the *last* server operating system capable of doing FRS. With the release of Windows Server 2019, you must be running DFSR.
The good news is that there is absolutely nothing to buy to convert from FRS to DFSR. There is no downtime. The entire flip should take less than 2 hours. If you haven't done this yet, I encourage you to get this done.
If you'd like us to do this for you, give our office a call. We'll get it scheduled and done.