Bots usually do SEO, so they need to post real links. Obfuscated links won't help their purpose, so they don't even bother with this. On our forum, you can post links after you have 4 posts. If links gets abused for spam purposes after the 4 post count, I can just install another mod which adds "nofollow" to links from users under a certain level of posts, breaking SEO tactics again.
If the link is useful though, I don't see any problem posting it.