Shaman - Chaining Cani Spells w SGSE?

[kb2005]

So I was searching for threads on canni dancing for funsies coz I'm that type of nerd, and I found some references to a canni technique involving the Shrunken Goblin Skull Earring, like this one from Skinned:

"Use a goblin skull earring to chain cast two levels of canni to burn away a lot of health for some mana on a clutch."

After reading other comments mentioning the gobby earring used in conjunction with canni dance, I'm still a little confused about what the utility of chaining two levels of cannibalize with the earring is. If you can cast them both and sit before the server tick, do they stack? If not, then what is the benefit?

(Also so it's clear I do understand the utility of using SGSE to reset global cooldown. That part I get.)