I worked with a guy who liked writing little <10 line functions, deeply nested, in dozens of files. Each individual function was nice and easy to read but figuring out what the entire call tree was doing required hours of archaeology.

Edit: He also refused to ever delete any code he'd written "because it might be useful later." I once spent three hours tracing the source of some values, only to discover that the output of the entire call tree I was working my way through was being quietly thrown away at the end.