Hi Mikeg,
Indeed for the moment the Smode Output is hardcoded into Smode Synth, so you can't really disable it.
What you can do however is change it's resolution to something very small such as one by one px.
You are right that this is not quite optimized and being able to kill the main output would be good to save GPU resources.
I created an issue in our internal issue system, but having other users asking for it could help raising priority: Users, if you agree with mikeg suggestion, please let it know by liking his post!