As I mentioned above, if the module is expressed as a code extension, then it is, sort of, "free." It is compiled into the main code body.

But, for example, say we are talking about a communication module. One module may use a well-known library as a bundled dependency, and another module may use the same one. They may be smart enough to use dylibs, in which case, you have the potential for "DLL hell," or they may use static libs, in which case you have duplication of code, and maybe resource contention.