Site Collections or Sub-Sites

Currently I’m working on Sri Lanka’s largest SharePoint implementation. According to the structure and the requirements of the project, my plan was to go for Site Collections. Specially the capacity and security. But I always like ideas from my team members which is helpful and knowledgeable in many different ways.
One of my team members Dinusha, came up with this article by Steve Goodyear.

Determining Between SharePoint Site Collections and Sub-Sites.