As some others explained, I feel it is a way to express satisfaction about the show on the ice.
As someone who attends 7-8 games a season, I will cheers good plays, I'll boo when I'm unsatisfied, but when it's great showing by the team leading by a few goals (usually 3+), I usually like to start the chant and people do like to follow up when it happens.
It's fun, as a fanbase, to have a little something unique, that we can use to express satisfaction about the performance "on-site", and easy enough so the entire fanbase can participate in.
I mean, it is not mandatory to have one, or it could be something else, but man it feels more enjoyable that way...
Granted, lately, I don't sing it as often...