Which benefits are included with Software Assurance for Microsoft SQL Server 2016?

High availability (only Standard and Enterprise edition)

• passive instance do not need to be licensed
• requirements:
  • there may only exist one passive instance for each licensed instance
  • the passive instance may not use more cores than the active instance
  • as a company, the passive instance may only be hosted in the Cloud

License mobility (only Standard and Enterprise edition)

• SQL Server licenses may be reassigned to different servers within a server farm as often as needed
• requirements:
  • licenses may only be reassigned to a different server farm or to a non-private cloud once every 90 days (Exception: permanent hardware failure)

Sources:

Microsoft Product Terms, August 2017
Microsoft SQL Server 2016 Licensing Guide_as is 2016-08-28