I've found comments are best for saying:
this link might help you out....
Comments with links are also useful if the OP hasn't really phrased his question explicitly and you want him to read the link to help him refine his problem. After reading your linked comment he might say
no my problem wasn't the floppy disc was upside down. I don't have one of those 5 1/4" real floppy disks. I have one of those 3 1/2" sony compact hard case floppy disks. Then you can get the "ahah!" moment and can post an answer tailored to his problem or comment with the exact link he needs to solve his problem.
Comments have restricted formatting (Ctrl+Altl+T may not work for example). Comments also have a character count limit. If you have a lot to say, or you wanted it presented in an easy to read format you must pick Answer over Comment.
As far as the up-voting answers goes, comments can be up-voted too. I don't see that happening often though and I believe the points are less. (Edit 1: ElderGeek points out flagged comments probably have zero reputation points) (EDIT 2* Zacharee1 confirms 0 points with certainty)
The advantage of taking a correct comment with a link and posting as a correct answer with a link is the OP can flag the question as solved. This is important for those in the future with the same problem who search and skip over questions not marked solved.
Tonight I had flagged a post as duplicate. Then realized it was slightly different than the duplicate. So I retracted the flag and posted an answer referencing the link with explanations of how his question was different than the link. As fate would have it after that I came here and read this question...