Though I usually don't have useless constants in a void context, I might use that sort of construct for loop control (among other things) if you want something else to happen before the control statement, and you don't want to waste space on a whole 'if' block, e.g.:

$success = 1, last if something();

# And I know TMTOWTDI but you get the idea
$success = something() and last;
last if $success = something();
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