It wasn't intended at all. I started out with the postfix for loop and then though, reduce would avoid the temp var and modified the line, leaving the *= behind.

That said, it does appear to run approximately 20% quicker which might come in handy some day.

To be completely honest, *= is just a short hand for

$total = $total * $_;
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Yes, I understand what *= does; the point is that reduce { $a *= $b } produces the same result as reduce { $a * $b } and the latter expresses the intention better (but the former is faster).