said 6 months, 2 weeks ago:
@julihanshaw There are two camps on that. One, you want to be able to give everyone the chance to comment, even if they find a post a year old. Some people find it frustrating when they want to comment on something but can’t.
Two, the longer you leave the comments open, the more spam you are likely to have to manage. If that isn’t an issue, then leaving the comments open shouldn’t be a problem. I left my comments open indefinitely up until earlier this year when I couldn’t handle the amount of spam. The issue is that the older the posts are, the more SEO value they have to people who want to comment to build links, hence older posts are hit way more than newer ones.