I think most of us operate with a single org. Perhaps the original concept from PTC never panned out or they opted for simplicity over complexity. What I remember when I was starting out is that you could effectively have multiple entities operating in a single system and not see each other. I think there is an option (but not sure its hard coded this way) that Parts in one org can be unique to that org. That means you can have part XYZ in one org and the other have the same part XYZ and those parts be different. Obviously, workflows, access rights, etc are split and can be different at the org level. Add in the complexity of file vaulting and locality, adding multiple orgs might be just one more thing to deal with.
When I re-read this post earlier today, I thought of the larger reason why most installs are single org. For many, the ultimate aim is to have collaboration, data sharing and commonality across sites. Yes, when we brought in new sites, there was that period of integration where they might want a slightly different workflow or access rights. Perhaps their roles were different or CAD system. That can be accommodated easily in a single Org. But, those differences can be broken down over time and in the mean time, you are leveraging the common parts and a methods. Throw in the business changes that occur very often of sites being bought, sold and merged and you want to be as flexible as possible when designing your PLM system. Just my 2 cents for what its worth.
