The quidelines for editing say don't change the meaning. And it's reasonable and just. But what about questions like this one: "Should I buy webcam of 720p or VGA quality?"
The first part, where the user asks whether he will benefit from 720p webcam on 64 kbps network, is on-topic and useful. The second part is a shopping question and obviously off-topic.
Now, should I just edit the post, killing the second part and changing the meaning, or flag the question or just comment and ask the user to do the editing?