- Redirecting the visitor automatically to the new location of the web page.
- Providing a 301 redirect [moved permanently] to search engine spiders.
- Setting up a username and password to access a part of or whole of your website.
- Restricting access to your website for all visitors originating from a particular IP address or IP range.
... and so on and so forth.
I have always found editing the .htaccess file as bit of a black art. Mainly because mastering the regular expressions involved to accomplish tasks takes a bit of practice and some hits and misses before you get the desired results.