As an example, one of my worst debugging sessions involved open's scope. Imagine you have a generic open_file() function in a script. The function uses a bareword FH, because whoever wrote it wasn't thinking about scope, they were just making sure a file was "open" (kinda related to the counterpoint you mentioned, that person might have learned enough to get by but not yet realize all the implications of what they were doing). Sometimes, deep in the code, you might open *another* file while processing the first one, leading to some bewildering action at a distince bugs...