Should I allow links in post comments box?
I think we should not allow to add link in comment message box because spam chances on website are higher if you allow links in comment box. During post a comment by user on any of post, by default wordpress send a notification to admin with post link so admin can easily know the comment post link by notification email or admin can check the comment post link from admin as well. Mostly time you will see that spam user always posted their website links to divert the traffic from your website to their website, so it’s not good for SEO purpose as well. So I can say that "the best way to avoid spam, and also for security reasons to never allow links in comments". By default, people can use email and I think that is you don’t want to hurt your SEO rankings, you should disable that too.