That applies to many warnings, yes... but not necessarily to those listed here. Personally, I can't easily recall warnings 'undef' ever having caught an actual problem in my code1, but it's constantly complaining about cases where nothing is wrong aside from my not having bothered to add an explicit default-to-zero or test-for-defined whose sole purpose is to shut warnings 'undef' up.
in reply to Re: Four annoying warnings
in thread Four annoying warnings
1 Which is not to say that it hasn't ever caught an actual problem for me. I'm sure it has done so on at least several occasions. But they're so rare that I can't think of any offhand.