WordPress is an excellent blogging engine. It is easy to setup and even easier to use. It has got a huge collection of themes and plugins. Because of all these things WordPress has got so widespread use.
WordPress has the concept of categories to segregate posts in different types.Â When number of posts in some category becomes really huge, its good to make a separate website for this particular category.
I faced similar problem for one of my website and I decided to migrate all of my posts in â€œXYZâ€ category to a different domain.