I tend to prefer command-line switches (I use --DEBUG). You can then conditionally load modules as appropriate using require or eval (you could of course, build your conditional using your $I_AM_DEV, but I personally find command line switches far more elegant and less annoying than modifying code to enable/disable such things). Example:

use Getopt::Long;
my %OPT;
GetOptions \%OPT, qw/ help|h DEBUG / or ($OPT{help} = 1);
if ($OPT{DEBUG}) {
    # whatever you like:
    require Data::Dump;
    eval "use Carp::Always";
}

...

say "Got some data:\n", Data::Dump::pp(\%my_data) if $OPT{DEBUG};
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