it's a standard sort of question in that it personalizes an issue and shows that there are not always black and white answers to difficult questions
absolute statements ("I would never use torture") can be tested by extreme cases, so that "I would never use torture" becomes "sometimes I would use torture"
e.g. your wife has been raped and murdered, do you support the death penalty?
e.g. your wife has been raped by her troglodyte half-brother and is carrying his demon seed, should abortion be illegal?
If a terrorist were in custody who had planted a suitcase nuke somewhere on the eastern seaboard but we didn't know where, yes I would torture him (or her) to try to find out where it was
Yes, but the suitcase nuke story is a strawman scenario. In real life, you don't know there's really a suitcase nuke (as opposed to some fools talking as if the device exists), you don't know it's on the Eastcoast (it may still be back in the home country), you don't know if this guy planted it (he may be some minion who bought an empty suitcase at Sears on behalf of someone else), you don't even really know the guy's a terrorist (you might be torturing some innocent person who's only crime is the color of his skin or the spelling of his name).