Lumen maintains running containers for each module in your stack in each point of presence on a per environment basis. That means that if you assign www.example.com and www.demonstration.com to the same Lumen environment, the same containers will handle traffic for both sites. If you have a new site that has similar needs and configuration patterns to a site that is already running on Lumen, then assigning both domains to the same environment greatly simplifies the overhead of managing them.
When two sites have the same URI patterns for resources and routes that should and should not be cached (i.e. both are set up for HTML caching and use the same routes for admin functionality or checkout), then it often makes sense to assign both of these domains to the same environment.
It is even possible to assign two domains to the same environment when the websites are running on different origin servers. Lumen supports routing requests to alternate origins based on the incoming request’s hostname or other criteria.
If the websites are mostly the same but have a few important differences, you can manage this as well within a single configuration by building hostname specific logic into your Varnish cache configuration: