In the game a lot can be done with souls, especially regarding the Shadow Isle champs. Souls can be used to restore mana or unleashed to deal damage
. They can also be harvested for some AP and armor 
or eaten to restore some health 
. In more extreme cases souls can be enslaved 
or replicated 
or bound to someone (Kalista). Why are there so many different uses for souls? What is the extent of their power?
High Lord Blaze2 votesA soul is worth a small value of Armor/AP that decreases as the game goes on
7ha7guy7772 votesi thought they changed it so souls always give .75 ap and armor
High Lord Blaze1 votesHmm, maybe they did. I don't know. I'm not too fussy about numbers.
Blood Mefist1 votesThat may be the case of Thresh, but why are souls also used by other champs in very different ways? Such as being re-summoned to serve in the case of Mordekaiser or used as a source of damage and mana sustain in Karthus' case?
Pinker 102 votesThe worth of a "soul" is about 21 grams.
whups, that's weight.
Blood Mefist1 votesP_P
PeterPanSmackMan2 votesSo like if you add 2+2, then you get 4. And if 4+4 = 8, then how does 8+8=16? doesn't that mean a soul is worth 6 because 16-8-2=6. BAM. SCIENCE
Shíny2 votesA soul is worth much , but that doesn't mean all those that wield the divine power of souls are proficient in their use.
There are those that revel in only the pain of the soul never grasping the entirety of the power a soul holds.
While others are overwhelmed by the souls they collect (kalista).
Some bind souls to relics never questioning their power nor seeking to gain more .
There is one though that knows the beauty death can bring and so knows the power of the soul, the one piece that passes over through that purifying moment of death. .
TL;DR Everyone uses souls differently as they're just tools to those that know how to use them.
Blood Mefist1 votesThank you, this is the kind of response i was looking for.
ULTRAF0RCE1 votesProbably not much a few of my friends from highschool bought some for free.
Rextreff1 votesCloth armour gives 15 armour and costs 300 gold. This means one armour point is worth 20 gold. Amplifying tome gives 20 ability power and costs 435 gold, which means one point of ability power is worth 21.75 gold. Since one soul gives Thresh .75 armour and ability power, a soul that Thresh collects is worth 31.3125 gold.