SSMS is supported for managing SQL Server 2008 through 2016 (except for SSIS instances which sadly still require a version-specific SSMS at the time of this writing). If you manage numerous servers on different versions, this unification is fantastic. There is partial support for managing pre-2008 instances. And, of course as you’d expect, the newest SSMS release supports various new features in SQL Server 2016 such as Query Statistics, Live Query Plans, Compare Showplan, Security Policies for row-level security, and so on with all the new 2016 goodies we have.
SSMS also supports managing Azure components such as Azure SQL Database and Azure SQL Data Warehouse, as well as hybrid cloud features such as StretchDB and Backup to URL. This additional unification is really, really handy.
I have a copy of SSMS 16 for reading Query Store, but not all of my plugins have been updated yet, so I’m still living in SSMS 2014 for now.