Thanks!
I had ideas about using them to power an attack by the drone where it would spear through the enemies. In the process it would disconnect the tail so you’d have to recollect the crystals. Didn’t have time though.
As it is right now all they are used for is handing to the altar in the middle of the map to progress to the next level. That, and giving the altar some crystals can trigger a bit of health restoration.