Also, it adds ongoing costs to change management, as now you have to modify two environments for each change, test two environments, ensure data is refreshed in

Also, it adds ongoing costs to change management, as now you have to modify two environments for each change, test two environments, ensure data is refreshed into your non-prod environment (while ensuring you don't use production data in it), monitor two environments, pay licensing and support costs (hardware and software) for two environments, etc. Having a secondary 'test' environment isn't as easy as 'oh just clone the VMs'.