SecurID Agent for Windows and XenApp

Could you please explain what the "Streamlined Authentication for Citrix XenApp" GPO setting does.

If we have a Server which has:

• Agent installed
• Agent configured to Challenge Users in a Group
• "Streamlined Authentication for Citrix XenApp" set to Enabled

If a User connects to the server via XenApp would they still get challenged for SecurID credentials if they are in the "Challenge Users" Group ? If so, is there anyway to stop that happening ?