Board Thread:General Discussion/@comment-24490850-20140201001833/@comment-1268838-20140209031202

While he hasn't expressly used them, their source is undoubtedly still present, seeing as "Hollow Ichigo" is his Zanpakutou. They were of significance when he turned out to have Fullbring, and those powers ended up fusing with his Shinigami powers.

It's just speculation, but I think that it was just Kubo's way of make Ichigo not have to slap on that damn mask every time he needs more power.