Full Mana when beginning your Fireburst would be a acceptable reason for me... **
but that´s a topic they will discuss eons..
In T8 for example, where you do mostly single target
-> I cast Blizz3 as opener (precast, so it hits exact at the pull)
-> T1 just for the proc-chance and the mp refill
-> Fire3 and there we go...
Thus, I am starting with the DoT up, Full MP and fastest way possible in my Firephase...
In Add phases, like when the Dreadnought spawns, I try to time it to be in UI3, and cast 2 times a T1 on both, instead of one T2 -> DoT Damage on both and increased Proc Chance...
** and for the mathematics who adjust piety so you have right enough MP left to Blizz3 -> T2 without being dependant of the Tick...
Spoken like a true teamplayer ^^
If you really try to impress, do the "Firework rotation" (name to be copyrighted)
Fire3 -> Flare -> Convert -> Flare -> Transpose -> Flare -> Flare -> Transpose -> Flare -> Flare -> Transpose...
this makes funny shiny lights, unfortunately, most mobs don´t survive ´til i am up for my 4th Flare...