Record enabled or monitored tracks are processed in realtime, the rest is pre-processed by ASIO-Guard. It doesn’t turn off but this track will simply bypass ASIO-Guard.
Unlike the driver buffer, ASIO-Guard does not add latency but permits to reduce it.
It does that by separating real-time tasks from those that need to be processed.
The two are then calculated in parallel by the CPU.
Since ASIO-Guard works on a buffer, it adds a delay between manipulating Effects, Instruments and MixConsole parameters and hearing the actual change.
It does NOT add input/output latency and only serves to relax the real-time processing, mainly when there is a lot of automation being read at the same time.
ASIO-Guard is only used during playback and permits to use a smaller buffer while reducing dropouts, and thus, having a lower latency.
ASIO-Guard is completely ignored when exporting or rendering the audio as this only relies on the main buffer.
Additional info here :
And here :