Why Service Applications?

One of the big structural changes in SharePoint 2010 are Service Applications, the successor to the Shared Service Provider model in SP2007. Now, service applications are part of SharePoint Foundation 2010 (successor to Windows SharePoint Services). And, there is a many-to-many relationship between service apps and web apps.  That means that a web app can consume one or more service apps, and a service app can be consumed by one or more web apps.  The easiest way to understand this would be some examples:

• Managed Metadata service app, which manages taxonomy and content types across sites, collections, apps, and farms.  You might have an enterprise term store with the enterprise taxonomy, managed by IT. Another term store may contain taxonomy for Finance, and perhaps a select group of users or managers in Finance manage that term store. The finance team site can consume both the enterprise and the finance term stores.
• Search.  You might have an intranet search service with search scopes that include Exchange public folders and file shares, as well as all of your SharePoint sites; and another search service that indexes a subset of SharePoint sites. Your extranet sites for partners may consume the SharePoint-only search service, but your intranet team sites may consume both the extranet and intranet search service apps.

Pretty cool, eh?  Can you see how interesting this might get?