It is very useful when you work with a lot of similar posts. So, when you copy a post, you don’t have to enter all metadata, taxonomies etc. each time manually.
If you don’t use an antispam plugin, you probably have thousands of spam comments. Most of them left by spambots.
Simple enough and step-by-step tutorial about protecting your blog.
How to remove default metaboxes, how to create your own custom metabox on the fly. The complete tutorial.