I think what you should generally strive for is a question-answer pair that in itself is consistent. That means: Imagine you're a visitor who doesn't know about the process behind writing this question and answer. What would you rather like to see?
- A question with an answer that fits the state of the question. Both seem to be written in one piece.
- A question with multiple
EDIT: paragraphs added, and an answer that does the same.
- A question with lacking details, only found in the comments (same goes for the answer).
I think we can agree that the first option is the most desirable.
If you can, always update your original post. In the case of a question that means to always include the most recent information, for example if there's a comment asking you for clarification. This does not necessarily have to be a ton of
EDIT:s added. In many cases it would make more sense to reformulate the question – if and only if it helps others (new visitors) to understand it better.
As an example: Why should you mention "Edit: I uninstalled the old version XYZ before" at the bottom of a post, rather then mentioning it where it fits chronologically, e.g. right at the beginning of a post: "I uninstalled the old version, and then tried to install version XYZ".
When everything's up-to-date, commenters asking for clarification can be notified, and if they've seen the changes, their comments might also be flagged as "obsolete" – I've been doing this many times in order to remove … well, obsolete information.
For an answer, the same thing applies. Make your answer consistent in itself and with regards to the question. Always update the post, and reformulate if necessary. Don't clutter it with
The whole point is: Make it easier for those not involved in the evolution of the Q&A to understand what's going on. It can be very hard to comprehend the timeline behind subsequent edits, clarification comments, etc. Remove the clutter, and we'll all be happy.
This really looks awkward, does it? Why can't the important information be in the answer itself? Update the answer to include everything we know, and then eventually delete the comments.
This looks strange too. The question is hard to understand, and it could be restructured. My point is: I don't care about the fact that the OP edited the question (I can see it in the revisions, if I want). All I want is all the information the OP can give me. It doesn't need an
EDIT appended. And it certainly shouldn't be buried in a comment somewhere.