Beside build consideration, you get a bit more performance out of headers-only libraries and single, large c files.

That technique is used in sqlite. https://www.sqlite.org/amalgamation.html

> Combining all the code for SQLite into one big file makes SQLite easier to deploy — there is just one file to keep track of. And because all code is in a single translation unit, compilers can do better inter-procedure optimization resulting in machine code that is between 5% and 10% faster.