all is in the title... but also related to Unanswered and abandoned questions So : is it good to give "clues" in comments as this will lead (probably) to unanswered questions ?
I cant speak for why everybody does it, but this is what I've seen, and done myself.
I leave an "answer" as a comment when I don't want to write a full answer, simple as that. There can be many reasons why I don't want to write a full answer: I don't have time, or don't feel like writing a full answer; I may not be 100% sure that what I'm saying is correct; I may not be sure of what the OP is asking and on and on.
Now "simple" questions may get answered in the comments because (people like me) don't want to take the time to write a proper answer when we can just say in one line what the OP needs to do. Yes I know we would be forfeiting the easy rep. (That may sound crazy to you now, but after you have used SE for a few years you'll see what I mean.)
Along those same lines, people may answer in the comments because it is so simple, they can't think of what more to write to make it a full answer.
It is completely up to you whether you leave "clues" in the comments.
Do bear in mind even if you "answered" in the comments and are coming back later to write a full answer your comment does not "reserve your spot." It is perfectly ok to write an answer off of somebody else's comment. (there is a lot on the SE metas on that topic)
The super short of it:
A comment is different then an answer, as such it is a courtesy to wait for the other user to come back and answer. When you answer it would be nice to mention the comment.
I would highly recommend that you do mention the comment if you wrote your answer based off of that comment. (but that is a different issue, count all that last part a bonus.)