There are many business environments where copying the data is effectively intractable so you need to run all of your data model operations in a single instance

There are many business environments where copying the data is effectively intractable so you need to run all of your data model operations in a single instance. More data models have this property with each passing year, largely because copying data is very slow and very expensive. This is not a big deal if your system is designed for it, sophisticated database engines have good control mechanisms for ensuring that heavy reporting or analytical jobs minimally impact concurrent operational workload.