Thank you @Fubar for your answer. I accept the general advice.
Let's assume my accounts and contacts live in a production environment A, together with a model driven app that uses them. And now I want to create a Power Pages site.
Should I create the Power Pages site in environment A, so the site can utilize all existing accounts and contacts, or should I create the Power Pages site in a new environment B, so it will have its own dedicated environment, and then duplicate all accounts and contacts? Eventually, I do need to use these accounts and contacts for both the existing model-driven app and the soon-to-be-created Power Pages site.
Thanks again,
Gil.