Recently I've come across questions which received some good comments but no answers. From the OPs' comments it was clear that the other comments had solved their problem. So practically each of these cases is an instance of a successful use of this site, but technically we have one more unanswered question, because since the OP's problem was solved, no further answers can be expected. Should the OP be encouraged to answer the question him-/herself using the hint in the comment, or should the user who wrote the comment be encouraged to write up a full answer? Or should the question be deleted (because it was probably trivial if it could be answered by a relatively short comment)? Or is there yet another satisfactory solution?
I think the comment's author should be encouraged to write a full answer even if they think it's a trivial one. Alternatively, someone else can answer the question giving credit to the comments.
I feel that sometimes comments discourage other users from answering a question because they think that the question has already been answered. But comments are not intended for answers, so I see no shame in writing a short answer in such a case.