The plugins available for WordPress are very effective and extremely convenient. Essentially, you can give your blog the ability to do anything. You can use plugins to link your blog to tumbler, make it more SEO friendly, clean unwanted content on your date base, and so on.
But, adding more features to your WordPress is just one aspect of the deed. There are plenty of free or paid plugins, meant to increase the level of security for the same. This includes being able to create a strong backup for your database, with the help of plugins.
Popular plugins are conveniently listed on the main site, but if you are struggling with a specific challenge, there is likely a plugin or a widget available for that as well.
Regardless of whether you are running a personal blog or a commercial website, they can be very handy, especially in regard of improving the search engine performance of your website or blog.