Every now and then in the Hinterlands a bear comes out and attacks the your party from a side, which can easily kill a couple of characters if you are no more than lvl 5. Flashfire has a panic effect that I found to be the easiest and fastest way to get rid of the problem. Since the bear attacks alone, panicking him gives you the time you need to put your tank on his way. Also, while he comes back (a few seconds of panic will have been enough for him to get quite a distance), you ranged characters will have time to deal some extra damage from a safe position. I saw no reason not to start those early bear fights with flashfire.
There are 2 areas were bears spawn. The west side, where everything is level 8 and rifts are level 12, and the mountain above the hoursemaster. If you rush up there you might get bears at level 5, if you are unlucky. However, it still leaves the question why you would want flashfire up to that point? At level 5 I would go:
Chain Lightning/Winter's grasp
Fade Step
Energy Barrage
Immolate
Flashpoint
either
Pyromancer
Fire mine
or
Clean Burn
Wall of Fire
Fire Mine hits bear for 1k non-crit at level 5. Fire Wall is just superior to flashfire in every way.
Do not argue with Matth85, he is a numbers/min-maxer, who cares only for the most number-efficient way to play, not knowing that one could easily play how they want the early levels then min-max once they get their specialization (which is less important that gear, and more important than party tactics).
The way I see it, the problem with mages is not the mana, but the spells themselves. Unless you are a knight enchanter (post-skyhold+), it is not simple, as you have to contend with cooldowns a lot. Immolate has 16 seconds, but Fire mine and Wall of Fire have 24 and 32 respectively. Casting those may not be that helpful in the long run. Early on, for both mana and cooldown (and thus damage) efficiency, it is best to stick with three points into the fire tree (immolate, flashpoint passive and, clean burn passive) and go for the cheaper spells all around.
Well aren't you cosy.
You do realize early levels are the hardest part of this game, and which is the only time minmaxing is remotely interesting, right?
That said, Flashfire is useless not because of minmaxing, but because of its design. Let's run down with it:
Low damage, long CD, high mana cost(!!), average panic(I found this unreliable). Chain Lightning is a better CC early game, Winter's grasp is a better combo early-game and ability points are few early game. As a mage you really want to get a few things:
Chain Lightning or Winter's Grasp.
Fade Step
Clean Burn
Energy Barrage
That is already 6 points taken. This means you either start of by being in flashfire and do mediocre damage early on, or you go Immolate and do pretty solid aoe damage.
It's not a question whether you can use it or not -- of course you can. It's a question whether it is useless compared to every other spell. Which it is. By the time you meet bears you can have Wall of Fire, which is directly superior to flashfire in every single way. If you are not afraid of bears early, you can go fire mine and kill them in record time due to their fire weakness and high damage of fire mine.