What are the alternatives:

my $foo;
if( $baz ) {
    $foo = $bar;
}
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Or

my $foo; 
$foo = $bar if $baz;
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Of course, if you're setting $foo, then presumably your gonna use it at some point later. And unless your enamoured with testing every variable for undef prior to using it, then in most cases there is a sensible default that it can be initialised to. In which case:

my $foo = 0;
$foo = $bar if $baz;
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Of course, that can be done "long hand" also if that's you preference.

And that's the point. Using this particular flaw in the Perl semantics as a justifiction for a style preference is disingenuous.