The above replies are all well and good, but they're mostly telling you what references are good for. Since you just asked what anonymous variables are for, I thought I'd provide a more direct answer: brevity.

Simply put, there's nothing you can do with an anonymous thing that you couldn't just as well do with a named thing. For example, to create a reference to a hash of arrays I could:

  my @array_one = (1, 2, 3);
  my @array_two = (3, 4, 5);
  my %hash = (one => \@array_one,
              two => \@array_two);
  my $ref = \%hash;
[download]

But it's so much nicer to be able to just say:

  my $ref = {one => [ 1, 2, 3 ],
             two => [ 3, 4, 5 ]};
[download]

-sam

PS: Actually, it occurs to me that this isn't quite true with subs, since you can't do 'my sub foo' and get a lexically scoped sub named foo. As such anonymous subs are your only way to make new sub routines at runtime without resorting to eval.