I like to run with warnings on. But sometimes I don't see them, like for instance, when I was editing a fairly substantial mod_perl script, which printed a whole bunch of stuff to the log, hiding any warnings in the scrollback.

Because I didn't see the warnings, I spent some frustrating time trying to discover what is going on in code that went something like this:

  my $some_index = 0;
  while ($thing = $thingies->next) {
    my $some_index = $thing->something_or_other;
    last if (test_for_fitness($some_index));
  }
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Yeah, I had originally declared the variable in the loop, but then I realized I would need it outside the loop, moved the declaration out, and forgot to remove the inner my. The loop worked perfectly, but the moment the program left the loop, $some_index was restored to 0 again.

And that is why I like perl warning me about a re-used my declaration.

I know it's not what you asked, just some food for thought