When to cast Flurry?

[Itsmesoft]

Mod edit: Moved to Q&A

So I was watching a stream on Twitch the other day with a top tier Frost Mage (don't remember his name) and I noticed that he doesn't cast his Flurry at the same time as me.

I do it like this: I cast a Frostbolt (we call this the first Frostbolt) that proccs Flurry, I will see this procc halfway through the next, following, Frostbolt (we call this the seccond Frostbolt) and will then cast Flurry asap after the seccond Frostbolt is finnished casting.

What I saw this Mage do was this: He cast the Frostbolt that proccs Flurry (first Frostbolt) and then after the seccond Frostbolt, instead of casting Flurry, he casts a third Frostbolt before he casts Flurry.

Why does he do this and what is the correct way to do it?

I hope you guys understand my post, my English isn't the best

[Imaskar]

Was he with water elemental? If yes, he maybe wanted to proc FoFs from pet freeze. But idk why, it's better to do it without BF procs.
Maybe he wanted some Chain Reaction before dumping a lot of Ice Lances.

[Itsmesoft]

Nope he did not use Water Elemental

[DeathDefier]

No reason to ever cast an extra frostbolt like that unless he was saving the proc for something important like for example a nightorb on Guldan.