If you are using it with Studio One enabling “monitor” on an instrument track will pass the MIDI input to the MIDI output. ThIs is effectively the same a THRU. If you are using it with another DAW, this is often called MIDI ECHO. You typically don’t need MIDI THRU on your MIDI interface because the routing takes place in software. THRU is common on synthesizers and sound modules because they are daisy chained off the MIDI interface. Each synthesizer or module listens on its unique MIDI channel and ignores the MIDI stream on other channels. THRU is used to pass the MIDI stream from your computer through all the of the synthesizers and modules in the chain.
