Using relics to make monsters do more damage

Hi,

I've been keeping differents relics that help monsters in various ways.

What's the point of using them?

Is it like "mapping"?... where affixes on your waystones upgrade the rarity and quantity of the loot.

Will a relic with let's say: "monster do 15% more damage", give a benefit or it's just a "fun" challenge to overcome?

(I know the unique relics dropped by Zarkoh gives special drops)...but what about all the other magic or unique ones, where it's just about helping the mobsters?


Thanks