My problem always is often when writing a function to remove duplication brings up the question of where to put it. If its only called inside one module doesn't matter really. But if not you've created a dependency. Which is bad.

I think how much you hate that may depend on your language and the program. Some big enterprise Java monolith is a garbage dump of thousands of small files. So who cares. In C without name spaces and the need for headers you care more.