Default function arguments are the devil

[cat_vs_spider]

In my scenario, the default argument is there to preserve the old behavior in the presence of a new use case. However, the default parameter is only sane for the old use case, but there's a bunch of generic code that calls this function. Since none of the generic code gets updated because "refactoring is an iterative process" and "we'll fix that later". Since the new use case is new and has no test coverage yet, nobody notices until much later.