It de-ataches CV from gate. It has de same effect as going FUNC + CV Gate link, and de-activate the tracks.
For example, you have the following sequence:
STEP 1-active 2-inactive 3-inactive 4-inactive 5-active 6-inactive
CV C1 D1 E1 G1 A1 B
If CV and gate are linked CV will only change on step 1 and 5 because those steps are active.
If CV and Gate are un-linked, CV is no dependent to the active step to it will change in all the steps.
It is a common use when, for example, you are using the gate output to control a drum module, and you are not using the CV output, so if you un-link that track you still can use this CV output to modulate any other thing.