Am I right in thinking the following about the Freeze Synth function in Sonar? :
- it turns my MIDI synth track into simple WAV audio and applies all the effects etc to that audio so the DAW has much less to process?
- And if you need to edit the synth track you can unfreeze and go back to its original state?
 
Bascially it converts the MIDI track into simple audio track...

Yes, although it is possible to freeze without applying effects. That depends on a freeze option setting.

I prefer to not freeze fx (unless there's an especially hungry plugin in the bin like a convolution reverb), since that limits your mixing options later on. The main reason for freezing is to lower CPU overhead and, in the case of samplers, to reclaim RAM. For effects such as compressors and equalizers, there's little benefit to printing them in the bounce.

But unfreezing again is easy.

jpetersen
But unfreezing again is easy.

One needs to remember, that then you lose all the possible edits you've done to the audio - unless you've copied it to another track.