Here are some 30+ case studies I found on HashiCorp’s website for Terraform: https://www.hashicorp.com/resources?content_type=Case%20Study&product=Terraform

I like this book chapter as one of the best arguments for using Terraform: https://www.oreilly.com/learning/why-use-terraform

Here’s the Mozilla case study the author was referring to: https://www.datocms-assets.com/2885/1509734354-mozilla.pdf