: Your average junior enlistedman today has immense responsibilities ranging
: from defense systems to intelligence gathering. Imagine if Bradley Manning
: wasn't in-league with Wikilinks, but was rather captured by the Iraqi
: insurgency or Al-Qaeda.

Quick answer at the end of my post... I tend to jump all over the place when I talk so if you wanna save yourself time... just scroll on down sonny.

For some reason I read this like some 40's tv show that explains military jobs to kids back then. You know... the kinda stuff that was sorta serious when it was made but is kinda comedy material in the present day. I even imagined an "Oh Boy!" in a kids voice after the first sentence when I read it... Don't judge me.

On a serious note, while those are legitimate reasons to keep prisoners, remember to the covenant we are 'vermin', unworthy of being absorbed into the Covenant. This is the Covenant that even allowed the Ungoy(sp?) to join their ranks. Technologically speaking they were far superior. As warriors only Spartans, Demons in Sanghelli tongue, were considered to be noteworthy(I do recall Elites acknowledging the tenacity and honor of the average human soldier, but still not a worthy challenge). Of course humanity has hit the jackpot several times over a short time span recently so one could argue that the scales have tipped or at least are tipping to humanities side. Plus, if we follow in the wise words of Halsey(I still am kinda torn at how Karin Traviss and 343i is portraying her, ruined what Eric Nylund created her to be) humanity should start thinking about using low level enhancements on at least soldiers. The S-IV's were enhanced without being the pick of the genetic pool so the UNSC must have this ability...

Back on topic... To answer your question I personally believe it is the fact that humans are identified as Forerunner artifacts. It's the same reason why they find our worlds at such a spectacular pace, which is because majority of Covenant ships have Forerunner Artifact scanners/probes/detectors and humans appear as artifacts. However, if they covenant were a couple shades more clever and didn't have a devious leadership, it would be noticed that humans are marked but not as artifacts, but each human is designated with a symbol representing 'Reclaimer'. Since the covies are in fact not a few shades more intelligent, and they do have a devious leadership, they probably take a few prisoners to try and discover where humans are hiding the artifacts and also to avoid being branded a heretic. I say this because an elite who knowingly kills all humans therefore all of what they believe to be 'artifacts', is heresy as far as the Council is concerned, but if they capture a few 'artifacts' and accept that others destruction(death) is unavoidable collateral damage they would probably receive praise and avoid being decreed a heretic.

Short answer... The Covenant more than likely takes prisoners due humans being designated as Forerunner Artifacts by the special equipment most Covenant ships carry. With the Covenant Hierarchy deciding to bury the truth that they are marked as 'Reclaimer's and not as artifacts, well let's just say anal probing by aliens probably turned into a reality for many a prisoner due to covies being dumbfounded as to where the humans hide the artifacts on their person.