"trag'oul's corroded fang"

my understanding of “TRAG’OUL’S CORRODED FANG” is that you have to use the skill “Grim Scythe” to get the effect out of the scythe ? i have seen this item in so many build but noone use the skill what so ever, what am im missing ?

Trag’Oul’s Corroded Fang

The Cursed Scythe rune for Grim Scythe now has a 100% chance to apply a curse and you deal 150-200% increased damage to cursed enemies.

It’s used because cursed enemies take 200% extra damage, i.e. triple damage. This means that even though you’re not using Grim Scythe to apply a curse, any way you apply a curse to enemies will grant the damage bonus.