XCode Project
The package is a little helper that allows you to add additional settings and parameters to the XCode project during the Unity post-process phase.
For example, if you have an IOS plugin that requires some flags, frameworks, libraries, or pList values to be added to the XCode project, there is no need to add it manually every time or making a post-process script. Just open plugin settings and do it visually.
And sure thing, there is a C# API as well, which you can use anytime from your Editor code.