Post answers as an answer. Post it (or expand it) later if you're on the phone and need to post/produce graphs and similar
TomMcW asked me the same question over the weekend in chat, so I'll repeat my answer here, and expand a bit on the reasoning.
TomMcW posed the following scenario:
When you have a possible line of reasoning, but you don't know if it's correct or you can't find a source, but somebody else might know of one
to which I replied:
I think I would keep it as a comment, but at the condition that it is not even a partial answer.
Q: What is the regulation for X?
Ok comment: I don't know, but I have searched here with these keywords.
Partial answer: It is somewhere in PartYY.
That is, for me we should accept comments that help find the answer, but not comments that (however broadly) contain the answer (or attempt to, as in "I think that ...").
This does not mean that partial answers should not be posted. It is still an answer! You can explicitly mention that is only a partial answer, but it is much better than posting it as a comment: it is more readable, anyone can edit it and expand it, plus, it can be properly (up)voted. Plus, you can always come back later and expand it with all the information you think is needed.
Another case posed by kevin in the comments to his answer is
for that particular question you want to use diagrams or quote past incidents or quote regulations. I am on my phone so I can do neither of those. E.g. the comment might be "Do X and Y". The full answer might be "According to the B737 Manual, we do W followed by X. If X does not work, do Y and Z"
In this case, as said here, it is no problem if you decide to post the answer a bit later. I guess you don't have only your phone to visit this site, so if you wait until you can post an answer with diagrams, or quoting past incidents or regulations, it is not a terrible thing.
If you think you won't be able to do it for a long time (say, weeks), and you really want to give this information, we go back to the previous case: post it as an answer. It is much better than a comment.