WordPress has a wonderfully unique feature called Multisite. It is a way of running a single install of WordPress while creating a network of websites on the same domain. It was introduced into WordPress with the 3.0 release. It is the way in which WordPress.com is functioning.
The way multisite works, you can create simple to very complex networks of sites. One of the interesting approaches that has started to come about is using a WordPress multisite to create a SAAS (Software as a Service). One you may be familiar with is Hello Bar.
The Genesis Framework Google+ group recently had a Hangout On Air to talk about Multisite and adress some of the groups questions. There were a couple questions that really drove the discussion and I wanted to highlight those discussions here.
Should you use Subdomains or Subdirectories?
The reality is that there is no “right” answer to this question. It really depends on how you plan to use the network. A general guideline that was suggested in the discussion was to use subdomains if you need or want to use domain mapping.
When Should You Use A Multisite?
There are very specific times when using a multisite is a very good option. During the discussion, we pointed out that when you have a network in which all of the sites are going to require similar resources, a Multisite would be a good solution.
For example, if you were going to build a SAAS for restaraunts, a Multisite would be a good solution. You will have the same kind of needs for all the sites on the network. This will help make sure your not extending options beyond what is needed, which can make the network unstable.
To hear the whole discussion, you can watch the recording here. If you have additional questions or comments, please ask in the comments below.