How to Determine when to splite a site into a site colleciton

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:

• Dedicated Recycle bins
• Dedicated usage Reports
• Distributed administration (site collection administrators)
• Dedicated search scopes, keywords, and best-bets
• Custom feature deployments
• Dedicated language translation maintenance
• Dedicated galleries for web parts, master pages, content types, site columns, site templates, and list templates
• Dedicated shared libraries, such as site collection images and site collection styles
• Dedicated real estate (Self Containment)

For the IT Administrators:

• Site quota templates
• Distributed administration
• Site locking
• Database maintenance options
• Backup / Restore abilities
• Content Deployments
• InfoPath forms services global template targeting
  

I have 2 big, at least what I think is big, points on why to use site collections. The first one is site quotas and recycle bins. The issue is the recycle bin is based on site collections and the quota for a site collection. If everyone shares a site collection, then they share the recycle bins storage size. The example I usually give is HR deletes 1MB per day and IT deletes 1GB per day. With a 5GB site quota, HR content will be flushed through the system a lot quicker if they share a recycle bin. This results in having to restore a database to get back a single document. (You know it will happen, Murphy’s Law). If they were in separate site collections, then the HR recycle bin would be valid for months maybe years with a 5GB quota because it is only affected by their deletions.

The second point is distributed administration. For most small companies this might be a moot point, but for high content driven organizations with a small IT force. It is a godsend for IT.