Having multiple marketing engines within a single business leaves you exposed to the risk of inefficiencies in spend. By having a single centralised system that drives every brand / business unit / franchise you can build it once and deploy it tens, hundreds or even thousands of times at a fraction of the cost. Think of it like building a single machine with multiple pipes, rather than lots of machines all with one pipe.
By having one system to drive them all you can give just the right level of control / editing rights to each user. It may be as simple as ensuring any assets released follow the same structure or branding, or it may be that you want to automate some of the business processes being followed by each user (e.g. document creation or customer management).
Future updates can be made once and deployed to every user / site / microsite in the system significantly faster than if every entity had its own independent website. This means you can use tools and features across the business much more easily. What's more, any bug fixing is limited to the one environment, so the testing phase results in a much more reliable end product.
As your business grows your website can become much more than a marketing front end for the business. Our most successful 'sites' have become advanced portals for managing all sorts business functions, most commonly accounting, user management, partner management, lead generation, marketing automation and business process automation.