The nega-psychic and the arcanist are the only character classes that are impervious to P.P.E. vampirism. No arcanist or supernatural being can use the P.P.E. of a nega-psychic or arcanist
pg 159
the poltergeist's syphoning of potential psychic energy from humans is painless and harmless (unless you're a mage who needs his P.P.E. for magic)
Arcanists are usually the only guys I think of when I think of spellcasting, but I guess this might be talking about how on pg 98 it also allows Parapsychologists to cast spells? Relates to 62's "understanding the principles of magic".
Sounds like both the arcanist and nega-psychic might have the equivalent of an always-on version of what would later come to be called the super psionic power PPE shield? This is a benefit I can't remember any other mages having, it seems extremely useful with poltergeists always entering the planet any time there's a rift or a summoning happening, to be immune to them.
I guess that means that while poltergeists would harass most magic users (food source) arcanists would be an exception since they'd realize they couldn't feed upon them.