In the Terminator franchise, extermination camps are often mentioned. But from a machine-logic POV, wouldn't it make more sense to just kill all humans on sight, period? Or herd them into small areas and nuke them? (even today's military electronics are hardened against EMPs and Skynet wouldn't care about the environment.) IIRC, the reasoning behind ghettoization / concentration camps / extermination camps / gas "showers" is to misdirect or mislead people both inside and outside the country as to what was really going on. But Skynet doesn't have to worry about bad publicity, and can manufacture all the free labor it needs. Is there any in-universe explanation for keeping large groups prisoners?
The original script for The Terminator suggests that they were death camps. The implication is that the aim was to dispose of the humans with as much efficiency as possible:
Kyle: Most of us were rounded up, put in camps...for orderly disposal...Some of us were kept alive...to work. Loading bodies. The disposal units ran night and day. We were that close to going out forever...
In the novelisation for Terminator: Salvation, we learn that Skynet also attempted to extract information from some prisoners...
So they kept moving, continued to follow wordless directives, and speculated on the manner of their impending demise. Options ranged from the abrupt to the fanciful. A few fatalists even pointed out that their deaths were likely to be less painful than the destruction humans had inflicted on other humans down through history. Where people had all too often proven themselves sadistic, willing to inflict pain for pain’s sake, the machines were only efficient. Except in isolated instances where there was a specific desire to extract information from the otherwise reluctant prisoner, no machine would kill by torture. Not because they regarded the use of torture as immoral, but because they considered it an inefficient allocation of resources.
And it also appears that it had been conducting medical research on their human prisoners, presumably in the hopes of creating a more believable Terminator infiltration unit.
Everything except the blood that was draining off a metal table in the room’s center. Its smell contrasted sharply with that of the otherwise all-pervasive disinfectant. The latter was of course unnecessary for the protection of the machines. They made use of such chemicals because they did not want their specimens to become contaminated.