what is "loopback check " is actually and what is the problem if we disable this

LoopBack Check is one of the security options that are coming with latest windows operating systems. It is enabled by default. It sometimes affects the Search Crawling as the crawler try to access the site which could be in some cases may be a WFE also. Ideally in development environment Disable Loop Back check is disabled my making entries manually in Registry. You can get lot of articles on doing that in the Internet.

Thanks

http://www.harbar.net/archive/2009/07/02/disableloopbackcheck-amp-sharepoint-what-every-admin-and-developer-should-know.aspx

http://www.harbar.net/archive/2010/02/12/groundhog-day-configuring-back-connection-host-names-using-group-policy.aspx

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