[flohofwoe]

You also need to consider that (at least in C++), your own code is just a very small snippet dangling off the end of a very large included stdlib code block, and that's for each source file which needs to include any C++ stdlib header.

For instance, just including <vector> in a C++ source file adds nearly 20kloc of code to the compilation unit:

https://www.godbolt.org/z/56ncqEqYs

If your project has 100 source files, each with 100 lines of code but each file includes the <vector> header (assuming this resolves to 20kloc), you will compile around 2mloc overall (100 * 20100 = 2010000).

If the same project code is in a single 10kloc source file which includes <vector>, you're only compiling 30kloc overall (100 * 100 + 20000 = 30000).

In such a case (which isn't even all that theoretical), you are just wasting a lot of energy keeping all your CPU cores busy compiling <vector> a hundred times over, versus compiling <vector> once on a single core ;)