Karune wrote:Nydus Worm prior to BlizzCon
Prior to BlizzCon, the Nydus Worm had to be summoned from the Nydus Canal, and only on creep. Thus, in order to do a drop, an Overlord was usually needed to drop creep, and then the Nydus Canal could spawn a Nydus Worm at that position. Also, because of the cooldown, typically for a mass drop, a Zerg player would need multiple Nydus Canals, to spawn multiple Nydus Worms at the drop position, to make sure the enemy couldn't easily destroy the Nydus Worms before the Zerg army could come out.
Nydus Worm at BlizzCon
In the BlizzCon build, the Nydus Worm no longer is spawned from the Nydus Canal. Additionally, it no longer needs to be spawned in on creep as well. Instead, the Nydus Worm is spawned in from the Overseer, and is based on energy cost. Thus, if you have multiple Overseers, you could easily spawn multiple Nydus Canals (which will have a 'build time' before the worm erupts from the ground) and ensure a higher success rate of getting your units out.

Karune wrote:Since the Nydus Worm is no longer a unit that is controlled like a unit or moved like a unit, this visual challenge is no longer an issue. The Nydus Worm is now spawned, rather than given move orders.

Karune wrote:When units enter the Nydus Worm opening or the Nydus Canal, they are in the Nydus network. They can exit at any opening, including the Nydus Canal building. There is no actual "tunneling," and is actually more similar to loading units in a dropship. When all entrances/exits are destroyed, all units in the network will die, so if you are a Zerg player, make sure you don't let that happen