I've never frozen a synth. To be honest, I've never understood what it does. I have a track folder with all of my MIDI tracks and soft synths (Kontakt, Engine, etc). When I'm done composing and recording, I bounce each track to its own audio track, all of which are in a separate track folder for audio. 

After I've programmed EzDrummer and recorded all my guitars through either Line 6 POD Farm og Amplitube, as well as recorded other synth sounds, I usuallly bounce them when I move from recording to mixing, siply to "commit" to those sounds, just as if they had all been recorded live (Real drums, real guitar amps, real piano/strings/organs/etc.).
 
Just how I prefer to do it :)