According to this FAQ, users who just create accounts should be able to include up to 2 links in their posts.
Ours is a support community, and our topic template encourages users to include a permalink so that we can investigate their questions with more clarity. Some new users (but maybe not all? I can't tell) report that they can not add links to their posts, as in this example:
Do you have any ideas we can investigate?
It's possible they are pasting in a ball of text (error logs or something) with a bunch of URLs in it. That'd be my guess.
Out of the box, new users are limited to 2 links per reply. You can modify this in your Admin, Site Settings, as needed.