Moved Permanently – When you want search engines and end users to show new page instead of old one then 301 code used either through IIS settings for .htaccess.

OR in one sentence you can say that 301 redirects are used to permanently move a site to a new location.

Search engines do not apply any penalties to 301 redirects using .htacess file.

Many seo expert use to redirect old pages or old domain to new page or domain.