At their base, cyborgs have their brains rewired to be completely robotic. At the very least, only one part of the original biological function remains.
Typically, cyborgs are humans that have either died or want to become "immortal" by becoming a cyborg. Becoming a cyborg is typically cost-prohibitive, and the procedure effectively kills you. People who have died or have met an untimely vegetative state are the usual targets of becoming cyborgs.
Cyborgs are not usually treated differently than humans, since they are essentially humans. If possible, a person's personality is "saved" and then "reinstalled" onto the new cyborg, and they act as if they had before becoming a cyborg. If not, there are default character profiles that can be chosen, modified, and installed, in an effort to preserve the person's prior personality (as it is chosen to be preserved).
Cyborgs should not be confused with people with mechanical, prosthetic parts, however. The main distinguishing notion between a cyborg and a bionic person is that cyborgs' brains are almost completely mechanical.
Cyborgs are useful in terms of preserving their "souls" for uses a normal person would not be able to be used for. You can save a copy of yourself on a hard drive for later use, such as being placed in cold storage for arduous space travel. Their "souls" are able to be transferred among different locations and resume their goals elsewhere faster than a normal person would be able to travel. The only issue would be having enough units to receive a Cyborg's soul who wished to travel to the location at hand.