Can you elaborate on what problems that would cause ? 10k LOC may be a bit extreme. Although having everything in the same place makes it easier to refactor and maintain. Breaking something up adds complexity, and is especially bad if it entangles itself with other parts of the code-base. I'll take one well structured file over 10k files with circular dependencies. If something can be lifted out into a library, of course you should do so, but breaking something for it's own sake is bad. For example include files within include files. Or include files disguised as modules.