In drupal 6 when you wanted to handle stuff on cron you often created a table to store stuff that needed processing by some cron job later or at best you used the http://drupal.org/project/job_queue.
In drupal 7 we can use cron queues. What does it do? It helps you to store stuff that needs processing later on cron.
How to implement it?
For example we are creating organic groups which we use as subsites in our system. We want to fill these sites with default content. So when it is created we dont want the user to be waiting for that content generation or worse make him interrupt this process. So we have a cron queue to do the work.