Apache is massively popular right now and probably the leading web server software. As such it is a security target, and much development and updates happen regarding Apache security. .htaccess is a security method long used by Apache, although it can do much more than just security. The .htaccess file provides a lot of functionality, anything from redirects, to URL re-writing, to changing PHP settings or Apache settings, folder display settings, and password and IP security.
.htaccess is hugely popular and a great way of going about several important tasks on a website. Documentation is readily available on the internet, most features are very easy, and the features it provides are incredibly useful.