It allows

my $rv = $args{'Post'} ? $args{'Post'}->() : 1;
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to be simplified to

my $rv = $args{'Post'}->();
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Or if the return value isn't checked, it allows

$args{'Post'} and $args{'Post'}->();
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to be simplified to

$args{'Post'}->();
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(sub{} would have been sufficient in the latter case.)