@Rithy And now i can exhale. Phew.
Basically i think you may have an idealized view of warp powers [they generally just get called powers] so lemme read from a table of the likely bi-products of any use of non-trivial powers [lighting a cig or making flashing lights or levitating a handful of coins or changing the colour of your eyes].
There is a ten percent chance of one of these things happening when a sanctioned psyker power is used
Dark Foreboding - A faint breeze surrounds the area, giving nearby individuals an unsettling feeling.
Warp Echo - For a short period, any sounds cause strange echoes.
Ethereal Stench - The air around the psyker becomes either pleasant or noxious.
Mounting Paranoia - The psyker gets an itchy back, as if there is someone behind them.
Grave Chill - The area around the psyker becomes cold and frost covered out for several metres.
Unnatural Aura - Any nearby animals become frightened and attempt to get away.
Memory Worm - Anyone in the vicinity of the psyker forgets something minor.
Spoilage - Any perishable goods within several metres become stale and useless.
Haunting Breeze - Winds surround the psyker strong enough to move around small objects.
Veil of Darkness - The area becomes devoid of natural light for a few feconds.
Distorted Reflection - Any reflective surfaces nearby break or distort.
Breath Leech - The air in nearby individuals lungs becomes lost, causing them to pause.
Daemonic Mask - The psyker channels a daemon for an instant, causing them to take on a frightful appearance for a moment, but corrupting their body permanently.
Unnatural Decay - All plants in the area wither.
Spectral Gale - Very strong winds envelop the area, knocking people to the ground.
Bloody Tears - Images or statues appear to weep blood. Chipped wood appears to ooze blood rather than sap.
The Earth Protests - The ground shakes violently, causing a local earthquake.
Psy Discharge - Static electriciy fills the area, causing the psyker to float for a short period.
Warp Ghosts - Howling ethereal apparitions fill the area, flying around unnerving the living and potentially causing insanity.
Falling Upwards - Gravity reverses for a few seconds.
Banshee Howl - A very loud screech fills the area out to almost a kilometre, causing people to be deafened.
The Furies - The psyker is assaulted by an invisible force, causing himself and nearby objects to be thrown around viciously.
Shadow of the Warp - (not to be confused with the Tyranid ability) The world changes appearance, causing people to glimpse the warp for an instant. Potentially destroying minds.
Tech Scorn - All tech devices and weapons nearby malfunction or jam.
Warp Madness - A psychic backlash of emotion fills the area, causing nearby individuals to become frenzied and mad. Potentially causing further emotional harm.
These things are not under the psykers control
Furthermore there is a twenty five percent chance that instead of one of these the psyker is responsible for one of these
The Gibbering - Uncontrolled warp energy surges through the psykers mind, burning out their minds and driving them insane.
Warp Burn - The energies of the warp manifest, striking the psykers mind and stunning him temporarily.
Psychic Concussion - The violent energies knock the psyker unconsious and cascade outwards, also stunning those nearby.
Psy-Blast - There is a sudden explosion, casting the psyker several metres into the air.
Soul Sear - The psykers soul is overpowered by warp energy, scarring their spirit and preventing them from using their powers.
Locked In - The excess energy remains in the psykers mind, locking them into a coma until it is overcome by sheer willpower.
Chronological Incontinence - The psyker vanishes as time bends around them, they reappear a few moments later.
Psychic Mirror - The psychic power targets the psyker himself.
Warp Whispers - The voices of daemons fill the area, speaking into the minds of others and corrupting their souls.
Vice Versa - The soul of the psyker is cast out and swaps bodies with a nearby being for a short period of time, if there is no nearby other, the soul wanders the warp for the same period and returns slightly less sane.
Dark Summoning - A lesser daemon physically manifests for a short period.
Ethereal Storm - The excess psychic energy lashes the minds of nearby sentient creatures.
Blood Rain - A cloud of psychic energy envelops the area, causing storm winds and rain of blood. While this storm is in effect, any psychic powers in the area always cause perils of the warp
Cataclysmic Blast - The psyker is immolated with psychic energy, burning their possessions, equipment and the area around them for a few metres.
Mass Possession - Daemons reach into the minds of all living creatures over a large area for a period. Sentient individuals must spend their time mentally combating the daemonic influence or they fall to corruption.
The Surly Bonds of Earth - much like the Falling Upwards phenomena, however gravity is reversed over a much larger area for much longer. Lifting objects much higher into the air.
Daemonhost - One of the most dangerous perils; the psyker is possessed by a daemon, becoming an unbound daemonhost.
Warp Feast - The uncontrolled psychic energies rip a whole in reality, centering on the psyker; sucking him into the warp to be consumed forever.
These area just examples taken from the Dark Heresy book. Psyker powers are very powerful but even accomplished psykers will often only use them as a last resort. This of course does not mean you are required to care about the consequences, particularly if the char is engulfed in something of an addiction. I'm just saying its likely to result in death or worse sooner rather than later.
Fun reading if nothing else.
Mixtape Ghost N