I'm pretty sure this spell has the best "charges-to-price" ratio at 10-2 for Akachi which makes it sort of a Swiss Army Knife for her:
Better than Hot Streak with Spirit-Speaker: For the same 4 xp, Akachi nets 8 resources for 2 cost up front.
Cheapest way to pay off Angered Spirits: Each charge paid is "worth" only 1 damage, compared to 3 damage for Shrivelling (5), plus you still have 6 charges left afterwards.
For the same reason, you don't feel as bad sacrificing charges for Torrent of Power.
Of course you can still attack with it. Finish off whatever health remains after a Shrivelling attack (especially with Sign Magick (3)). Or if you've loaded up with Shrivelling (5), use this to pick off 1-2 health enemies.
Mix-and-match the above. Pay off Angered Spirits, pick off an annoying 2 health enemy, then convert the rest for a 2 resource gain. Or better yet, use up all the charges, then recall to your hand with Spirit Speaker and play it again to reload 10 more charges.
This probably shouldn't be Akachi's main combat spell as the extra charge from her innate is worth less than Shrivelling (not to mention the action loss risk). But it's a great "side arm" to Shrivelling or its equivalents, and is more efficient to use for the other purposes above. In this way, there's a natural upgrade pathway from Obfuscation to Brand of Cthugha (1) to Brand of Cthugha (4) for her "jank spell" slot.