"good interrogators don't need those techniques"- DIA agent laughed "at the idea that anyone would be so incompetent as to use any of these [torture] techniques." Rebukes Perino and would fire McConnell (Dir. Natl Intel) - Retired Army Lt General Harry E Soyster, Director of Defense Intelligence Agency during Desert Shield/Storm

It's not to gain knowledge. It's to make the prisoner compliant primarily and also punish.

I recall a quote from Oliver Stone's movie 'Nixon' :

Nixon shuffles back alone, coming to a stop in front of a larger-than-life, full-length oil portrait of JOHN F. KENNEDY. Nixon studies the portrait, pads closer. Looks up.

NIXON
When they look at you, they see what they want to be.
(then)
When they look at me, they see what they are ...