It's commonly used in runs, and was used the moment it was discovered, as far as any% is concerned we use the arrows from Andres shop to store the max quantity, and then use that saved value to duplicate the Soul of a Proud Knight we grab in the Valley of The Drakes, can confirm its known in the souls community :P

Edit: Good looking out though, if you ever find anything interesting that the souls community doesn't already know, definitely let us know!