From the Collector’s ed. book:
The First Ones who shaped the cosmos knew they needed to protect the Shadowlands from external threats and beyond. Maldraxxus was their answer.
Such was the original goal of it. But who knows if the way Shadowlands funcion is in line with what is supposed to be originally.
Maldraxxus exists to defend the Shadowlands against cosmic threats like the Burning Legion. Sometimes that takes the form of repelling invasions; other times, it involves a more proactive approach.
All these forces [cosmological chart] push and pull against one another in the balance of the universe.
If it would be needed, we could be able get there regardless.
For mortals to cross over into these other planes requires considerable effort.
Shattering the veil just made it easier.
https://worldofwarcraft.judgehype.com/news/interview-de-steve-danuser-sur-l-histoire-de-shadowlands-164320/
So, anima seems to be a source of power. Energy seemingly needed for void lords to sustain themselves outside of the realm of pure Shadow that exists somewhere outside the boundaries of the Great Dark Beyond (aka WoW “reality”).
Souls are the source of power for fel energies, and thus - could be of use for the Legion.
Life is not clear, it’s already heavily represented in the Dream and Ardenweald, which are “branches of the same tree” (first source).
Order forces are shady and it’s not really clear how the Pantheon so successfully was searching for more titans that we’ve never heard about a single one other than the original ones.
Light is unlikely to need anything there by default, and would not even appear [in Shadowlands] without actions of Denathrius (1st link). They are more about life in the universe, and it’s a thing of “reality”, not Shadowlands.
TL;DR: souls / anima might be a valuable resources. Ra-den claims that anima is one of tools for “creation & destruction” magic, whatever are the tools the Pantheon used to wipe out or create planetary systems.
gl hf