Only one word to add to previous, wise, answers: iterator. The diamond operator around your filehandle is an iterator.
High Order Perl book has a wonderful chapter about this and an implementation can be also found on Cpan.
When you search a number in your address book you prefere to learn all entries by memory and only after the last number dial the number you searched for (backticks), or descend the list until you find the number (iterator)?
hth
L*
UPDATE: link to the book as suggested by AnomalousMonk below.