Closures allow you to organize code differently. The resulting style is as distinct from OO and procedural as they are from each other.

Right now Dominus is writing a book on the subject. You can find some information in this article on iterators, a number of my nodes talk about closures a bit, see Why I like functional programming for one of the better ones. Or you can search for more information.

Of course in this case the technique is just for fun. A somewhat shorter implementation of a sieve of Eratosthenes is:

sub sieve {
grep{@_[map$a*$_,$_..@_/($a=$_)]=0if$_[$_]>1}@_=0..pop
}

print join " ", sieve(100);
[download]

(Implementation due to tye at (tye)Re3: (Golf): Sieve of Eratosthenes.)