I wanted to say a few things that may help when deciding upon when a Farm, Web Application, Content Database and Site Collection are necessary. For the purposes of this discussion I am defining a Large organization as any organization implementing a medium to large server farm. A small organization would be one using a single server farm.
First think of these items in terms of how we suggest implementing Active Directory:
Web Farm is Like a AD Forrest
Web Application is Like a AD Domain
Content Database is Like an AD Partition
Site Collection is like an AD Organizational Unit
Web Farm:
You need to consider separate Web Farms for Very Large Organizations where political or Very Large Implementations are needed such as separate Shared Service Providers(Max 8 per farm) are required.
Web Application:
Consider Web Applications when you need to define Zones and Policies that are unique.
Content Database:
The recommended limit is 100 GB. The main thought here is Disaster Recovery time and SQL Performance.
Site Collections:
In smaller organizations, separate site collections organized by business units is appropriate. In a large organization, I would recommend a separate site collection for each high level team. Focus your efforts upon building a wide rather than deep hierarchy. Site collections will allow the IT department freedom to maintain just application itself without the worry of security or content hierarchy maintenance. The following is a list of what an individual site collection offers.
For the Users:
For the IT Administrators:
Some good links to read that may help:
· http://www.sharepointblogs.com/llowevad/archive/2007/11/09/when-to-use-site-collections-vs-sub-sites.aspx
· http://www.sharepointblogs.com/llowevad/archive/2007/06/25/site-collection-logical-architecture.aspx