The compiler package allows you to manually edit the source files and compile them to a bootable structure, so any Skyline Application is able to boot from that compilation.
Skyline CMS boots from a compiled file structure.
The compilation allows it to increase performance while delivering your website, but also, detect possible bug before they occur.
When you are creating a project using composer, you do not need to require the compiler.
in fact, creating projects in development, includes the compiler package automatically.
$ composer require skyline/compiler
You can setup several configuration to automatically compile within your IDE, but Skyline CMS will not compile automatically.
Note that the compiler is not designed for performance, so you shoult not use it before responding requests.
In fact, using the compiler in your web application is only recommended inside the administrator panel where you can inform the client about the compiling process.