Makes your Haunt and Locust Swarm last 120,000 seconds (2,000 minutes, or almost 1.5 days), which is a necessity for anyone playing the Raiment of the Jade Harvester set to even deal any significant damage and can be useful for keeping up buffs such as Ring of Emptiness or rune effects like Locust Swarm Cloud of Insects and Haunt Poisoned Spirit / Consuming Spirit or simply the Piranhas damage amplification. The DoTs will drop when you move too far away (around 1.5-2 screens) and will have to be reapplied. Also, for Locust Swarm runes other than Pestilence, the visual animation will likely bug out after a medium amount (around 20-30) targets have been affected, the effects will still be applied however.
Top-tier passive for DoT builds
Must have for Jade, really good in general for anything that involves the mentioned skills and combinations. As a Ring of Emptiness enabler, you can choose useful runes that give you back some value lost from taking the passive on top of the comfortable infinite duration.