When you freeze a track, the track will appear greyed out. To freeze a track simply right click on the track and click freeze. Live will make reference audio files in your project’s folder both for session and arrangement view midi and audio clips. Because the track is frozen and is now playing audio files rather than generating a sound real time, your CPU usage is reduced. You can then commit a track by flattening, which just pulls those reference audio files back into your project, replacing any devices that were in the frozen track.
Consolidate will combine 2 or more clips of either audio or midi. To consolidate a clip, highlight 2 or more clips, right click, then click Consolidate Consolidate is NOT a way to reduce CPU. It is designed to simplify and clean up your project file. When you consolidate 2 or more audio clips, a new audio clip will be created that replaces the old. Likewise a new midi clip is created to combine 2 or more midi clips. Consolidate is ALWAYS PreFX. Meaning the devices on a track will still remain after consolidating.