One other reason I sometimes temporarily turn on diagnostics is to find out what keyword to use when I want to selectively turn off a particular group of warnings. For example, in this case yo see that the body of the diagnostic message begins with (D deprecated). If for some reason I wanted to turn off such warnings in a suitably narrowed scope, I would do this: 

use strict;
use warnings;
# ...
{
  no warnings 'deprecated';
  %hash->{ silly } = 'foo';
}

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Granted, I can't think of any good reason for turning off this particular warning (except perhaps globally on a large body of legacy code), but there are more realistic examples. E.g.: 
use strict;
use warnings;
require Exporter;
{
  no warnings 'once';
  *import = \&Exporter::import;
}

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The no warnings above silences a warning of the form 
Name "main::import" used only once: possible typo...

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Yes, one could silence this warning like this instead: 

*import = *import = \&Exporter::import;

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...but I digress.

the lowliest monk

In reply to Re^2: Unusual way of accessing hash values by tlm
in thread Unusual way of accessing hash values by drone

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