I just work this out.. but seems no point to use it

[Li Ngok Lam]

$x = sub { $y = shift; print $y };
$X = $x;
$X -> ("123"); # prints 123;
undef $X;
$Z = $x;
$Z -> ("234"); # prints 234

Question : 
1. When will you use this kind of style in your code ?
2. Any "name" for this kind of coding style ?

TIA