Watch this from The Matrix... specially at the 0:40 seconds mark...
Now, in The Matrix, humans are spawned in vitro, hooked to feeders for nutrition and 'feed' and illusion reality (to keep the human alive)... thus harvesting the energy the organism produce.
The Imperium is much MUCH sadistic. Imagine the Imperium as a HUGE bureaucratic machine. It makes the Start Wars world of Coruscant (bureaucratic planet center of the Republic, covered 1,000% of political and governmental institutions) look like Woodstock. If you are lucky, your job would consist about sitting in a small dark room, listening to numbers come out from a speaker and typing them to a terminal... never knowing what they mean or where they go. If you are good, you are rewarded... when you die, your corpse is re-animated with cybernetics so you can continue to serve... as a semi-lobotomized Servitor.
Now, like I put on the Corrupt Cherubim introduction, rich and powerful bastards delight themselves in showcasing Servitors... the harder to make and maintain, the better. The lowest form of cybernetic manipulation would be a non-sentient animal... like a Cyber Mastiff. Clerical Servitors are built from the bodies and brains of pencil pushers, while construction Servitors are made from criminals whose bodies succumb too early to their sentences of force labor. Literally, not even death will be a relief. It is rumored that some consciousness is preserved, but locked... incapable of acting. You just suck in the fact of an Eternity of Loneliness, trapped in your own body and mind.
The highest form of cybernetic manipulation is a young child, especially a baby. The popular idea is that babies (or children) who die early in life and immortalized a Cherubim. They are completely lobotomized (no consciousness) and are a pure reflection of human potential and the power within each person, as they serve the Emperor. It is also rumored that there are some babies are breed in vitro; the cloning process tweaked to produce beautiful bodies.. perfect in form and function.
A more nefarious method, always unconfirmed but never denied. Those who defy the Imperium, those who commit acts of great heresy do not deserve death. Remember... that is a reward
reserved for loyalists. So what could be worse that becoming a Servitor? How about watching your children become one... while THEY remain their consciousness and are very well aware that their fate is a direct cause of YOUR actions. Parents are tortured into watching siblings torturing the younger ones in preparation for the transformation.
Crap... I almost went REALLY dark. SEE WHAT YOU DO TO ME WOMAN?
Hope all that helps... I'm NOT sleeping today. Thank you...