Restarting the SQL Server Database Service and SQL Server Agent Services
Most Microsoft SQL Server configuration options can take effect immediately, but a few require the service to be restarted. To stop and restart the SQL Server service or SQL Server Agent service, right-click the service under Registered Servers or Object Explorer, and then click Start/Stop Service and Change Accounts. Use SQL Server Configuration Manager to stop and restart the service.
The following configuration options require restarting the service:
Startup parameters such as trace flags
Server authentication mode
If the password used by a service is changed, SQL Server can use the new password immediately.
Enabling, disabling, or changing the configuration of network protocols (using SQL Server Configuration Manager)