I freeze pretty much all tracks I'm not presently working on. It's just one click to either freeze or unfreeze to adjust as needed.
Here's a simple example. Add an amp sim to a guitar track. Then pile on some effects within that amp sim. That can end up as a serious CPU hit for just that one track if you really take advantage of a bunch of the amp sim's features. But, if you freeze it you get all the sound without a hit on the CPU.
Better yet, put the amp sim in an FX Chain bin in the ProChannel. Throw on some ProChannel modules and get the track sounding super awesome. Then freeze the track (one click). Again, you get all the super sound with no hit on the CPU. So including all the ProChannel processing and a full-on tricked out amp sim sound, you can end up with a simple audio track but which is totally optimized.
Rinse and repeat throughout the tracks of the song. At the end you still have lots of CPU room to pile on live effects in the busses when mixing and even mastering.