need some help/advice

[Ualaa]

I'd guess, there might be channeling spells on other keybinds, which aren't part of the default sequence.
By including nochanneling in the spam, the spam won't interfere with Drain Soul or Drain Life.

Either that, or its just being cautious, as nochanneling doesn't really hurt anything.
And you never know when you'll include a spell which utilizes channeling.

[Solon]

Ualaa has it right, I have other buttons for my channeled spells, and I may want to be spamming my DPS key for the rest of my team while channeling.