Suppose I asked a question in an area where I am no expert. Then the question is getting answers that point out that the question is ambiguous or has not enough information for a meaningful answer. Comments are added that discuss what the question might actually be, if it makes sense, how ambiguities could be addressed etc.
In such a case, would I start a completely new question "take #2", perhaps with a pointer to the old, confusing question?
Or adding a comment and clarifying. One problem with comments is that they have a size limitation and only limited formatting (no math formulae etc.) and that it's hard to find in the cloud of other comments. Users that see the question for the first time are likely to miss the one comment that adds additional information.