C language code is compiled and then it is run. just assume that the code is compiled. Obviously, the compilation of code will take some time. A small piece of code will compile faster while a large code will take time to get compiled.
In C language you can break your code and put it in multiple source code files. C language will compile the files separately and then link them together for execution.
This makes compilation fast.
Another plus point of this is, multiple programmers/developers can work on different code files while working on a single project.