It's sometimes tempting to put short answers into the comments section of a question, rather than putting them as answers. Stack Exchange site guidance discourages this. Instead, please post answers in the answer section, where you can later edit typos, make improvements, and get upvotes.

Using the comments defeats the functioning of the Stack Exchange engine. And since comments on the question go above real answers, it's a way to get in a first word, which is unfair to the real answers.

They also push down comments which might be used to get clarification and improve the question itself — which is the intended purpose of comments to questions. (See again the guidance linked above.)

If you have a good, succinct answer, please put it in the answer section. If you know that your comment is an incomplete answer, it's probably best to think about how to round it out. Or maybe just let someone else answer. (Or, if you really can't resist, think about coming back later after someone else answers and deleting your comment so it doesn't distract. Maybe it could even fit as an edit to another answer, or a comment to an answer, which is less harmful since at least the answer comes first.)

I guess I have mixed thoughts on comments like "Here's a youtube video on this subject", or "Google for foo and you'll see..." That's often pragmatically helpful, which is good, but... We're pretty strict about not allowing these as answers, but having those same things as comments doesn't solve the problems noted above. (Why does this get page-position priority over full answers? What if the video is pulled or moved and no one bit a mod can edit to fix?) I think it's really better to take the time to provide at least a brief real answer along with the link.

The main exception is when the question is clearly going to be closed (and as something other than a duplicate). In that case, comments can help the user and are really better than full answers (because answer on off-topic questions encourage more of the same). Should we encourage / allow comments with helpful advice to questions we know will be closed?

On several other SE sites where I participate, comments are regularly deleted by the mods en masse even if they're helpful. I like that we don't tend to do that here, but it does mean we should be more careful of starting messiness. I know I'm guilty of all of this myself sometimes so I'm not on a high horse or anything. It's something we can all do to improve the quality of our Q&A archive.