The case is simple: I asked a question. It got answered with all the information requested. Then I realized a little bit more info would be handy. Should I ask for it in a comment to the accepted answer ? Thanks
If it is a new question, ask a new question.
As it is related to another question, a link to that question would be a good idea, adding information.
Hiding questions in comments is not good practice - people don't see them. We also don't like the practice of getting follow on questions in comments. See this question about "chameleon questions".
Depends on the amount of info.
If it's a teensy bit more info, no problem. Otherwise, it should be relevant to the question--by relevant I mean that it should be helpful to solving the question.
Basically, ask yourself "Would knowledge gleaned from answers to this comment help solve the above question?" If the answer's no, then ask it as a separate question.
If the additional question is only to clarify a point made in the post then IMO that is fine. However, if you are asked a question that could essentially stand by itself then you should gently nudge the OP to post a new question (if needed). It all depends on the situation -
There are no rules here and you will not be punished for answering those additional questions.
On the bright side you'll be helping someone and that is a good thing - its what we're here for
I just realized that my answer was actually addressing the person who would be considering answering an additional question and not the asker. In anycase I hope the points I made shed some light on the subject and possibly help you to understand what might be going on the mind of the people attempting to assist you.