itemtype module position gives you the option to place a module in the content area. Ofcourse you can also use the module position-plugin in the default Joomla distribution, but thats not integrated in Pages-and-Items :)
The alternative is
www.pages-and-items.com/plugin-module-in-article/, which might be easyer to use, some people claim.
What to use a module in content for? well, you can position a login in between content, or a search-box, or a (custom) menu or a poll, just any module really. That just gives developers and designers a lot more options when making a site.