This is true, not only is it practical but it also makes a good rhetorical hammer, for example I once started an argument with a truther friend asking him what exactly he believed, "for instance, do you believe all the Jews were evacuated before the planes hit?". Forcing someone defending an irrational belief to first disassociate himself from all the really nutty stuff hanging on to his position works wonders.

I love this technique. It's fun to use on missionaries - I got a couple Mormons a while ago and was able to chatter excitedly about how I'd got this tenet and that article down because of other correspondences, but now they were here, and I'd heard missionaries had special knowledge of these things, and maybe they could clear up one or two points of confusion? It turns out that the best way to get rid of missionaries is to be sincerely sorry to see them go.

I agree. Actually, questions are useful at any time. When it seems like the person is changing their position without acknowledging it, I usually ask something like this:

"I'm a little confused. Before, you seemed to be saying X. Now, you seem to be saying Y. Which is it?"

If the person evades my question, that's the end of the debate as far as I am concerned. I have my own rules of debate, and one rule is that my opponent must answer reasonable questions so that I may understand his or her position.

You've got to be careful though. Some people, i.e. many creationists, will just take that as an invitation to ramble ad infinitum.