It is easy to set up whether search bots can or can not access a certain part of a forum. It can be configured from the admin panel.
The only reason people let bots crawl the forum, requiring registration for normal users is because they want to generate more traffic from people using search engines to find their forum, and if the forum requires mandatory registration for everyone including google, it's going be ranked really low on the list since there is nothing for it to crawl.
The only reason people let bots crawl the forum, requiring registration for normal users is because they want to generate more traffic from people using search engines to find their forum, and if the forum requires mandatory registration for everyone including google, it's going be ranked really low on the list since there is nothing for it to crawl.