If you activate this function when you click on a fret it will be as if you clicked on all the frets containing the same note on all octaves.
This is a quick way of mapping arpeggios or scales on a fretboard. For example if you click on the notes A, C and E, you will end up with a complet map of the triads of A minor on a fretboard.
You can use this function in conjuction with the selector to activate the octa-selector. Read more about using selector and octaver together.