If you are worried about your CPU and your system specs are lower than required it could potentially be an issue, but we do have a lot of folks who have success running MainStage on less than our recommended specs. Each 100% in the MainStage CPU meter accounts for 1 core (you may experience usage percentages over 100). If you are considering upgrading, check out our thoughts about computers.
The first thing I would check out is our tips about CPU usage here:
As long as you are not experiencing pops or glitches, then you should be ok- the percentage is somewhat misleading. Our suggestion is to really test you rig and push it to see what the limits are. Then you will know what you can comfortably and reliably run in MS. (This may mean backing up Sunday Keys, and in a duplicate concert, removing the patches you aren’t using).
Check out this video about us pushing MainStage's limits: