Stygia farm

There are several reasons to kill rares and events in The Maw:

Rares and events are a good daily source of  Stygia - With Stygia being a rare commodity in the Maw, rares and events are the best source for Stygia to purchase supplies from Ve'nari.

Rares and events are also a solid way of farming reputation with Ve'nari - Each event grants 40 reputation with Ve'nari, and each rare grants 60 reputation with the Broker. In addition, the rares have a chance to drop Maw Lore, items that can be delivered to Ve'nari for an additional 100 reputation per.

For achievement hunters, killing all available rares and events at the Maw grant the achievements  It's About Sending a Message and  Better to Be Lucky Than Dead. Retrieving Maw Lore also eventually completes the achievement  Deciphering Death's Intentions.