It’s new canon. Ahsoka novel and even the Darth Vader:Lords of the Sith comic. Specifically dealing with Sith lightsabers. In old EU red lightsabers were specifically non-organic and had no force sensitivity. In the new canon all crystals have organic properties and the Sith have to force their will on their crystal, making it “bleed.”
This is why Kylo’s blade is so interesting. My assumption is he went to “bleed” his original crystal but since he himself is conflicted inside the bleeding process did not take and the crystal cracked. Hence the need for the side vents. They were not intentional design decisions but a result of using his cracked crystal.