A modular application is well, modular, meaning that it is more like webparts or self contained applications that are included in an app. For example, say you are building a CMS, you can include a Guestbook, A forum, A blog and ofcouse the news module. Now not everyone wants all these features. Instead of commenting them out, you simply don't include them. You disable them, but hey are still there. Let's say 2 years later you change your mind and now want to include those features, you simply go to the admin section of your site and turn them on and bingo, they are available.
You also decide to only run one module of a big application. Take a look at Community server,it is a blog, a forum, Cms, Picture app etc. Most people only use the blog module. A truely modular application will allow you to rip any one module and run it as a stand alone application.
Ok, as for the Pros and Cons of BeerHOuse, it depends on how advanced you are. For a professional developer, you can use this TBH kit as a framework for a world class application. It is a well built tool designed to showcase the depts you can push .Net framework.
Also, with a little modifications, you can modularize it and use it for a very well built CMS.
For a beginner, the most you can learn from it is how to build good applications, assuming you uderstand C#,
Hope this helps
yousaid