Our rules state that if somebody does post a link, then we expect a reciprocal. Especially if it's a commercial link (for which we say they must ask permission) It's more of a polite request rather than a rule but it does mean we get some linkbacks so it's good to allow linking once you know the member. If they stop posting I might remove their links if I find them, but life's too short to go hunting them down.
It's a fine line between not being taken advantage of and having a useful site - links are what makes the internet what it is so we need them. In theold days of SEO there seemed to be a race to get as many inbound links as possible witha s few outbound links, but that seems to have changed. And before that all sites had a page of purely links, those seem to have mostly gone as well. Google may have succeeded in for a large part getting rid of link farms and paid for links.
It's all down to a nice balance and ensuring the outbound links are on topic and useful.
Many threads on my site feature links. My site is about trains, and lot of the content is news, especially right now. I have no problem with outbound links.
However, there's a difference between useful and spam. If you simply post "Hey, come check out my train photo page!", you're likely to get banned or at best the message will be deleted. However, is somebody on my page asks "So what's an SD70" and you post "It's a 4000 HP diesel electric built by EMD, etc, etc, and then add "I have a photo gallery of them at my page..." I'd be OK with that. Both are links to your site, but in is spam, while the other has added value.