Compilers often "inline" functions or unroll loops. This can make the C output look significantly different from the original source code, even if it is functionally identical.
The C output is much easier to share with developers or include in a report. 2. How to Decompile: The "F5" Workflow
Mastering IDA Pro: Converting Assembly to C with the Hex-Rays Decompiler
You can define structures and types to see how data flows through the program.