Configuration management (CM) is a systems engineering process for establishing and maintaining consistency of a product's performance, functional, and physical attributes with its requirements, design, and operational information throughout its life. - Wikipedia
Configuration management helps for the configuration of the software that will be running in an operating system ie Nginx installation + its config.
Infrastructure provisioning is the process of automating and provisioning hardware instances to run your software on. Example being the ability to automate the provisioning of EC2 instances on AWS.
Configuration management SHOULD NOT be used for infrastructure provisioning.
Benefints that infrastructure provisioning has over config management: