for aps classes like sins and BMs its helpful..
but for arcanes...its not worth it
if I went lunar cape for -6% channel on my wizard, I would have less than 30k hp (28k hp I think).
considering that we can be instantly killed easily, there is no point in sacrificing the crucial stats from a dragon cape for an extra -6% channel.
besides. If sharded correctly, you can get a -69% channel on a wizard (demons can hit -89% with demon wellspring quaff). which is good enough