The majority of the problems can indeed be solved that way. (Though good luck if you forget a local anywhere.) But there are more subtle maintainability issues with implicitly passing data in global variables. Code that is explicit about where data that is being acted on came from is better than code which hides that information elsewhere.

This is also why I dislike local. Oh, I know when to use it and I do use it correctly. But I prefer not needing it. Perl has too many scoping mechanisms whose interactions are too baroque. Rather few people really understand it, and when people are working with interfaces they don't understand they get confused and make mistakes. (Often without knowing that they made mistakes.) As the documentation says, local is probably not what you wanted to use, my is generally more appropriate...