Board Thread:Questions and Answers/@comment-10797017-20130622101437/@comment-11051098-20130622102933

Ukitake's Shikai has 2 blades because it can absorb an attack, like a Cero, and fire it back at the launcher while having the ability to adjust the speed and power. Whether it has 2 blades because it can absorb and return attacks, or whether it can absorb and return attacks because it has 2 blades, are unknown.

Kyôraku's Zanpakutô exist as 2 separate blades in it's sealed state. I think that's why they are also separate in it's Shikai.

As for Ichigo's new Shikai, it might be an offensive/defensive thing. According to someone's thoughts, the 2 blades might be connected with a chain in it's Bankai, allowing the small blade to be used as a long-ranged projectile attack, or a defensive blade to block/stop attacks, while the large blade is offensive with attacks like Getsuga Tenshô.