Here's the thing about Jinteki. Some of the time they're trying to kill you. And sometimes they just want you to suffer.
Sure, you have a few cards with the potential for a kill: Cortex Lock, Ronin, Snare!. But you also have a lot of cards that, while they hurt the runner, are unlikely to actually kill them. Psychic Field, Shock!, Komainu, Shi.Kyū, House of Knives, Fetal AI, Hokusai Grid.
The "Thousand Cuts" archetype wants the runner to bleed. It forces the runner to realize that they're going to lose somewhere around a third of the cards in their deck over the course of a game. Any tightly-wound strategy player with combo pieces that have to be held in hand, or anything that used cards as fuel (cough Faust cough Aesop cough Apex cough MaxX) is going to find themselves with very little left in their stack to work with.
This is where Harvester comes in. Forcing the runner to draw up to and past their maximum hand size means you are going to have a tough time killing them. But, if the runner was already at max hand size when they hit it, that means that SIX CARDS are going to get thrown in the garbage. SIX. That's 13% of a normal size runner deck.
Of course, that does mean that the runner can churn through their deck faster to find exactly what they need. And this is where your other net damage becomes really useful. See, against a thousand-cuts deck, a wise runner will hold their less useful cards in hand as a buffer so that suprise Snare! hurts less. But if you've just been Harvested, that isn't an option.
But this only matters if the runner is at max hand size when they hit Harvester. If the runner can absorb one of the subroutines without discarding, it doesn't look so great. As a result, Harvester does best in a deck that does brain damage or otherwise limits hand size. Pālanā Agroplex will also help you keep their hands full.