Board Thread:Warhammer 40k General Discussion/@comment-108.31.46.183-20150605045910/@comment-8881468-20150605194456

The souls are used to maintain the astronomicon, so basiccally psykers are merely fuel/nourishment. Bear in mind that the astronomicon was aorund before the golden throne and that psykers were already sacrificed on it in 30k (as we see in "the outcast dead" where the astropath fears being turned over to that device)  (if I read it correctly)

and as far as I can remember, the warp is the place for the emanations of all beings, aka: all souls go there and end up in the general mishmash ^^