The torture served an array of rhetorical purposes, and, according to this line of analysis, it served only rhetorical purposes.
According to Frank Rich,
The White House, Congress and politicians of both parties should get out of the way. We don’t need another commission. We don’t need any Capitol Hill witch hunts. What we must have are fair trials that at long last uphold and reclaim our nation’s commitment to the rule of law.
See Frank Rich, "The Banality of Bush White House Evil," The New York Times, 26 April 2009.
Rich provides several useful links to the relevant literature.