Thank you for your suggestion.
If i set to true of login_required setting, then all users has to do login the forum.
May be it hurt in seo like if someone come from google search engine then they has to login first to read the content.
Also, i have doubt regarding how google, bing bot crawl if i set to true. (they stop crawling my forum?)
It will be great if someone has set to true and share their experience regarding google and yahoo bot crawling.