Cold to Fire?

I am trying to understand the Cold to Fire support niche, and am not sure I am seeing its raison d'etre.

It seems fair to say that this gem is not envisioned to be used much with attacks, since one could just as easily slot an "added fire damage" or such, but rather with spells. But if I am using this with a spell, then I will gain no bonuses from "added cold damage" from gear (since these apply to attacks only); hence, it appears as if this gem is supposed to work with spells that do primarily cold damage. But if that's the case, when do I use this as opposed to using anything else that I would ordinarily use with a cold spell? I mean this: If I am using a cold spell, and considering converting some to fire, then either I have +fire damage passives or I have + cold damage passives (because otherwise, why would I use a cold spell?). If I have +cold damage nodes, why switch to fire? If I have + fire damage nodes, why use a cold spell?

I'm not asking this to complain about this gem or anything of the sort, I'm asking because there is obviously a use for it, and I would like to understand that. A somewhat lengthy reply would certainly not be overlooked by me, please feel free to elaborate.

Thank you.

If you are making a Glacial Hammer Templar/Marauder etc. you could get the lava lash passive which will make you do more damage.

Using cold to fire also gives your spells/attacks more diversified damage. This means if you are fighting an enemy with cold resistance, you will do more damage than without cold to fire. If you are fighting an enemy with fire resistance you still do good damage. It also allows you to proc both freeze and ignite with one spell.

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Vipermagi wrote:

When you Crit with a Cold damage Spell, you're easily going to get a long ass Freeze out of it. Kind of redundant really, after a certain point.
With Cold to Fire, you lose some excessive Freeze duration, and gain Ignite damage in return.

"If I have +cold damage nodes, why switch to fire?"
Converted damage also benefits from source-specific bonuses; the converted Fire damage will also benefit from Cold-only bonuses. It's never a loss in terms of raw damage per hit. :)

Ah, so the cold bonus gives me more cold, and THEN it is converted to fire? If so, then I get it. Thank you.

EDIT: But is it still "worth it" to use CtF instead of something like Faster Casting, LMP, AoE, Cold Penetration, etc.?

Wow, thanks. That's complicated. I had no idea +cold supports (and I'm guessing passives too?) apply to the fire portion. Interesting.

I suppose that makes it "worth it" vs. a support such as cold penetration etc... (?)

I made a build where i used this skill. You can read it here.

http://www.pathofexile.com/forum/view-thread/284205/highlight/

Sorry to pester again, but just to make sure I am understanding the math correctly: Fire-only bonuses apply to the fire portion of the post-conversion damage only, while cold-only bonuses apply to the entire portion (pre- and post-conversion)?

Actually, to ask another question, if I may:
- Suppose I had a bit of a strange gentleman, who basically went around attracting people with Enduring Cry, getting hit, and letting Molten Shell explode on them. This gentleman already had invested in a few + fire damage and +burning nodes. If, just if, this person were to cast Frost Nova all of a sudden, with Cold to Fire -- just as an idea, since he is already attracting the people with his big fat "target me" -- would he be better off investing in +cold or in +fire damage? Or, to rephrase, is his +fire nodes / gear (what if, just what if, he were already wielding The Searing Touch?) a reason in itself to use this gem in trying out Frost Nova?