How do C++20 Modules (.ixx / .cppm) compare to traditional .h and .cpp file structures? Do they actually eliminate header guards and speed up build times?

Modules compile once into a binary Module Interface File (BMI / IFC). When another translation unit imports the module (import MyModule;), the compiler loads the pre-parsed AST directly instead of re-tokenizing thousands of lines of text! Macro leaks across files are completely prevented.

Build times on large projects drop dramatically because header parsing is no longer duplicated across every single .cpp file.