I absolutely love Dark Harvest but i have to admit, I still don't get why it exists.
Its power is comparable to Electrocute only difference being Dark Harvest has infinite scaling and a slightly worse early game.
In some cases Dark Harvest just ends up being broken and in others completely useless. But in the times where you know you won't be doing as much with it you can just take Electrocute because they are essentially the same.
And the people you would think would benefit from it the most, farming junglers, typically end up being the worst users.
I mean, I guess one of the niche's is that it lets Assassins who "fall off" scale ridiculously into late game (SA
for example).