In Call of Duty: Black Ops 3, what do the rituals in the Shadows of Evil map actually do? Is there any benefit to doing them?
In addition to being the first step of a dark ops calling card, you need to complete all five Rituals to enable the Pack-a-Punch (Which allows you to Pack [upgrade, 5000 points] and then RePack [essentially enchant, 2500 points per "roll"] most weapons in the game). Even if you're not after the map's side quest, you will want to at least get the rituals done so that you can pack your weapons.
You do also get a small point reward (I think it's 500 points) for being in a ritual zone when the ritual is complete. This is per player, so in a four player game, if everyone is in the ritual zone, each player gets that bonus individually.