By default Enable-SqlAlwaysOn try to restart the sql server service if -NoServiceRestart option is not used.With -NoServiceRestart will make changes in the registery but it will only take effect once the Services re recycled.
--Standalone sql instance Enable-SqlAlwaysOn -Path SQLSERVER:hostname or instance name in case of named instance -NoServiceRestart --Clustered Instance Enable-SqlAlwaysOn -Path SQLSERVER:SQLInstance Name -NoServiceRestart