[clang] Question about the compiler invocations file for CTU analysis

I was reading the [documentation](https://clang.llvm.org/docs/analyzer/user-docs/CrossTranslationUnit.html) for the Clang Analyzer. It's not clear to me what is the purpose of the `invocations.yaml` file. The documentation says:

> The compiler invocation is a shell command that could be used to compile the TU-s main source file. The mapping from absolute source file paths of a TU to lists of compilation command segments used to compile said TU are given in YAML format referred to as invocation list, and must be passed as an analyzer-config argument.

But I thought this was the same purpose of `compile_commands.json`.