Links to other sites

When I have done some courses in SEO, links to other sites should be in 'no-follow' rather than a regular link. In that way, the crawlers wouldn't jump to that link, and start exploring that website.
So, I usually hide links from guests, so the crawlers wouldn't be able to detect links to other websites. Well, it's easy when compared to explaining this to the users, who don't seem to care.
What about you guys?
What do you think of links to other sites? Do you allow them? Are they regular links?