When shooting a beacon while standing far away you normally have to wait a while for the grapple to retract until you regain control: https://imgur.com/a/bLNVH1o

However, by tapping grapple, it retracts instantly, unless it hit a beacon.

If you now tap grapple the frame it hits the beacon though, it both activates the beacon and retracts the grapple instantly, saving the time you would have to wait normally: https://imgur.com/a/oag6zjN

Since this cancels part of the grapple animation, i would call it the "grapple cancel" :D

This allows for a major timesave in any% by rerouting after the top-right beacon, going around, skipping the very tight fast strat to normally get to the 3rd beacon, seen here:

On the other beacons the timesave is less major, since you are already close to them, exept the bottom-right one, on which this would allow to move off-cam even earlier at the end of Any%