MainStage is an amazing program. There isn’t another application out there that can do all mainstage can do. But it’s easy to set things up in a way that is not best for your CPU. I use mainstage every time I play And i typically get about 20-50% of CPU usage as I play. there are serveral things I’ve learned over the years about using mainstage live:

1. Don’t stack and stack and stack sounds on top of sounds…if you do map them to different areas of the keyboard..(map strings and pads above C-3 etc instead of all across the board)
2. If you use multiple kontakt instruments…use it multi-output mode as oppose to having several channel strips open and mute them instead of trying to bypass them
3. Another thing with layering…use your patch list and setup 3 to 4 layers for each song you play plus that helps you stay organized as oppose to trying to fumble for a button to try to reset your layers for each song you do…this way your layers and click tracks and stems are always ready to go at one click…
4. To conserve ram use an alias of a plugin that you use often…I use the MKsensation all the time so I have it aliased on all my patches
5. Increase your buffer…I keep mine around 256…some interfaces will allow you to go up to 512 without any latency..
6. Turn off your i/O safety buffer…when you get close to maxing out your buffer…the safety buffer increases it and decrease automatically to compensate latency…but increases cpu to do so
7. Turn off auto save…it can cause audio issues and midi issues during a background save
8. Use mainstage in performance mode and not edit mode…uses more cpu in edit mode cause it’s always waiting on you to hit save…
9.May sound crazy…but clean off your desktop…the desktop is basically the interface of Finder..and Finder renders all videos, audio and all files on the desktop for immediate viewing when the space bar is hit…a junky desktop will slow your computer performance way down and uses a lot of reserve cpu…I keep only a few items at most on my desktop
10. Keep your volume from clipping can cause CPU spikes… If you need more volume try to compensate by using your interface or amp as another gain stage to try to keep from peaking. Plus Audio distortion is not a desirable effect.
11. Watch heavy sustain pedal usage on build ups and “rolls” I ease up as I get into those…heavy sustain will push CPU
12. Don’t use a lot of heavy plugins on the channels…use aux buses and the sends for reverbs and delays…
13. Get a faster Hard drive and more ram…at least 8GB of Ram…and a 7200rpm hard drive