FSAA can be enabled independently from TA Spring; it can generally be enabled, on a Windows system, in your video card's control panel located in the 'Display' section of Control Panel (right-click desktop, properties). Then its the Setings tab, then hit the Advanced button. Then there is usually a panel for you video card and it can be enabled from there.
The only advantage of having it actually controlled from within the Spring settings is just that--it can be controlled from Spring's settings, assuming you have your video card's FSAA settings set to "Application Controlled."