A lot of companies are busy building greenfield environments — typically entirely new, separate network segments or Active Directory forests. Often, companies go to the expense of creating a greenfield because the current environment is so disjointed and full of accumulated errors that trying to fix the mess seems impossible. Security will usually be given more leeway and consideration, though not victory at all costs. It’s important not to repeat the same mistakes of the old environment in the new environment, says security expert.”]
Source: https://www.csoonline.com/article/2609655/7-essentials-for-creating-a-greenfield-environment.html