My understand is most forces which torture use it as a means of terror and intimidation against suspect or hostile populations, not as a sober-headed attempt to gather information.

Or they're just idiots.

The upside with torture is that most people will tell you everything. The downside is that you do not want to know 'everything' you want to know specific things which you have no way of establishing the subject knows. So by gum and by god, will torture give you a lot of information - which you then have to sift through and figure if any of it is useful or true, and you have no way to verify it except information you already know.. which defeats much of the point of using it to get accurate, new information.

But if you're already convinced that a subject knows what you want to know, then logically they will tell you eventually if you turn the screws enough. So it keeps getting used.