Just an amusing anecdote that came up in the session I ran last weekend, something that was very unexpected but ended up helping the Acolytes quite a lot.
Generally, upon reading the rules, I expected the Psychic Phenomena, from when a Psyker rolls a 9 on Focus Power, to generally be a negative thing. You're going to draw attention to yourself, you're going to cause people to freak out and either become uncooperative or attack you, etc.
However, in TWO cases in one session, the Psyker in my party managed to turn his Psychic Phenomena manifestations to the good.
SOME SPOILERS FOR EDGE OF DARKNESS FOLLOW
I'm running Edge of Darkness, and this was our second session. The group had already encountered and destroyed two of the Body Snatchers, so the Logicians were locked down and searching for them, although they had not positively identified the group as the culprits. As a result, the Acolytes had a pair of Enforcers following them discreetly when they went to visit the Templum. The Acolytes were aware they were being followed (succeeding on Awareness checks), but assumed it was just because they were armed strangers and there had been disappearances so the Enforcers were being cautious. Not wanting to cause a scene, and assuming they were not doing anything illegal, they simply ignored their tails as they went into the Templum to speak to Zed and Fayban.
When they LEFT the Templum some time later, they found those Enforcers waiting for them. The Enforcers at this point had weapons drawn, and demanded the Acolytes 'accompany them to the station for questioning regarding some incidents' the night before. The Acolytes were about to agree to this, not wanting to upset local law enforcement, until the Enforcers demanded they hand over their weapons. This didn't sit well, so the Acolytes decided to try and fend off the Enforcers. The Psyker Focused Power to use Forget Me, with the intent of making one of the two Enforcers suddenly forget why they were arresting these people, which if nothing else would give a moment of confusion in which the Acolytes might pounce. He rolled a 9 on the check, and so rolled again on Pyschic Phenomena.
The Phenomenon that manifested was the one that causes all technology in the vicinity to momentarily stop functioning. It doesn't give a duration, but says 'momentarily', so I ruled it to be about 10 seconds. Needless to say, for 10 seconds the area was plunged into total darkness, as this being inside a Hive (and poorly lit to begin with), technological lights are the only source of illumination! Thinking quick (and still right beside the Templum door), the Psyker then yelled "QUICK, OUT TO THE STREET" before, as quietly as possible, pulling his teammates back through the door and easing it shut. The Enforcers, predictably, turned and ran out to the street, assuming the Acolytes had made a break for it in the dark. The Acolytes, meanwhile, slipped out a side door of the Templum and escaped before the Enforcers realized their mistake and came back.
A little while later, the group encountered another pair of Enforcers down the street. These Enforcers had been tipped off by the first pair, and so opened fire immedietly upon spotting the Acolytes. A battle ensued, and the Acolytes won, knocking one Enforcer unconscious and wounding the other to the point that he surrendered. Tying him up, the Acolytes wanted to question him, but first the Psyker tried to use Healer on him, so he wouldn't die of his wounds and would be in better condition to talk. He again rolled a 9 on his check, so rolled Psychic Phenomena.
This time he manifested an unearthly gust of wind, which everyone managed to stand against (aside from the party's Tech-priest, who fell to the ground embarassingly). The Psyker, realizing what was happeing, combined the unearthly indoor wind with some suitably threatening speaking, and the combination was enough to terrify the Enforcer into spilling his guts.
So, the lesson we learned is, sometimes Psychic Phenomena can be your friend!