The SharePoint subwebs are used when your site is large. It is easier and more logical to break this site into multiple smaller subwebs. The SharePoint subweb is a complete SharePoint web with exactly same properties and features as any regular website, which is located in a subdirectory of the main root of the main website or another subweb site. This implies that any subweb can have multiple levels of subdirectories each housing a separate website.

In other word, the root SharePoint web site is the higher level directory of the SharePoint site collection and any subweb resides under this main root or under other subwebs.

The concept of the SharePoint subwebs is important when you want to architect your organizational structure in the SharePoint. For example, you may want to create one website and assign this website to be your organizational site and then all departments within your organization will become subwebs. Moreover, if your department is presented in different regions with its own heads then this subweb will contain other subwebs each dedicated to a specific region.

There are several advantages of setting up subwebs versus building organizational stracture within same website. First, each subweb can be maintained by different admin or group of administrators. Second, each subweb can have its own security paradigm. Finally, performance of the SharePoint is better overall when main web site is broken into multiple subwebs.

The SharePoint allows you to perform following operations on subwebs: create and delete subwebs, merge subwebs, recalculate subwebs, set permissions on subwebs. Howerver, there are limitations that you need to be aware as well. They are: administrative options are not available including subweb usage stats, health stats, document forums and subscriptions.

One of the major considerations for creating subwebs is a potential growth of your organizational structure over time in size and complexity.