Freeze is pretty much a useless spell right now, and almost always with the exception of certain level gaps being used as a brief filler in an aoe rotation (before you obtain Blizzard III). Crowd control is next to useless in this game, so Freeze really has no function at all whatsoever right now.
Now, at level 70 a Black Mage's AoE rotation includes Thunder IV, Fire III, Flare, Blizzard IV, Foul. Sometimes Fire II. I always thought it was awkward to include Blizzard IV in the rotation (necessary for Umbral Hearts for back to back Flare uses), and wondered why not use Freeze to grant an Umbral Heart instead?
Currently my AoE rotation I usually use is: Blizzard III -> Enochian -> Thunder IV -> Blizzard IV -> Fire III -> Triplecast -> Flare -> Flare -> Convert -> Flare -> Transpose -> Foul -> Thunder IV -> Blizzard IV -> Fire III -> Flare -> Swiftcast -> Flare -> Transpose
Of course that repeats and extra Thunder IVs get tossed in there with Thundercloud procs, etc. but I always felt awkward using Blizzard IV. It's necessary for Umbral Hearts unless you want to use the old method of just Fire II x2 -> Flare then you can skip Blizzard IV (or you have tons of mobs where the Fire II spam is more DPS than Flare and Umbral Hearts mean more Fire IIs). I just feel it would be cooler to have Freeze in there instead. Plus it keeps more AoE pressure up instead of having gaps in between AoE casts. So then I would end up doing:
Freeze -> Enochian -> Thunder IV -> Fire III -> Triplecast -> Flare -> Flare -> Convert -> Flare -> Transpose -> Foul -> Thunder IV -> Freeze -> Fire III -> Flare -> Swiftcast -> Flare -> Transpose
To me that would make more sense because I am keeping up an AoE rotation and it would feel and flow better to do so as opposed to stopping AoE to use another single target spell, plus it would actually make use of Freeze. Freeze is only 100 potency, so it's not like it would significantly increase AoE dps (well, only 3+ mobs starting slightly and gaining a bit as you have more enemies), and having it grant an Umbral Heart will still fulfill the purpose of allowing you to use back to back Flares. I say 1 Umbral Heart as opposed to the 3 that Blizzard IV grants because of opportunity cost. If you choose to use Blizzard IV, you should get more Umbral Hearts because you are sacrificing AoE damage for more Umbral Hearts. I would even be ok with nerfing the potency to 80 if dps gain is really a concern, I just feel it should grant an Umbral Heart.
Anyway, please make this change. I want to see Freeze be useful, and I want my AoE rotation to flow better. It would just be a neat quality of life change so I can use Freeze in AoE rotations instead of Blizzard IV, and have a reason to include it on my hotbar. Otherwise you might as well remove the spell from the game because it serves no other purpose. Freeze is an iconic spell. It makes me sad to see it totally useless.