Smart comments provide an easy way to insert debugging and tracking code
into a program. They can report the value of a variable, track the progress
of a loop, and verify that particular assertions are true.

Best of all, when you're finished debugging, you don't have to remove them.
Simply commenting out the 'use Smart::Comments' line turns them back into
regular comments. Leaving smart comments in your code is smart because if
you needed them once, you'll almost certainly need them again later.