Maybe I'm having a senior moment here, but I can't see how the statement in the OPed code
    sub { ... };
    # wander away...
can possibly do anything at all.

One could define and subsequently invoke a subroutine
    sub func { ... }
    # some other stuff...
    func();
or define and save a reference to a subroutine and subsequently invoke it
    my $coderef = sub { ... };
    # some other stuff...
    $coderef->();
or define a reference to a subroutine and immediately invoke it
    sub { ... }->();
but I don't understand the definition of the OPed code, which just seems to define a subroutine reference and then immediately throw it away.

Am I missing something?