I'm entirely new to Deathwatch and trying to figure out the purpose of the psychic "buff" powers, i.e. powers that improve your combat effectiveness, particular the ones that improve your ability in melee combat. They take a half action to manifest, and a half action to sustain as far as I understand. Which means that, if you do not start your turn in melee range, you cannot attack and have your psychic power active, since it would take a minimum of three actions (one to manifest/sustain, one to attack, one to move) to actually have your power active and hit someone.
So then what's the point? I suppose you can manifest and hope someone moves next to you, but that seems very counter-intuitive compared to how librarians are portrayed. I'm coming from other RPGs and tabletop 40k, where it is very possible to have buffs "going". In tabletop, for example, you can move, manifest and attack all in the same turn. The only other situation I can think of is using them in a protracted melee engagement, but it seems very limited use.