If you mute the regions on the track then you're saving all CPU & HD resources normally required to play that track.
To mute the regions, select them all (click the track header when cycle mode is off), and press Control-M (or click them with the Mute tool).
At the moment i'm turning off plugins and vst, not the midi/audio regions. Nothing saved in ram/cpu?
However
My problem's not the RAM, it can be CPU usage and HD (i'm on hdd 5400rpm, not SSD unluckily...) so i'm thinking: my problem is cpu...if i mute tracks, do it use the same cpu power?