I am using http://drupal.org/project/mailchimp
Module: 7.x-2.7
Name : MailChimp, MailChimp Campaigns, MailChimp Lists

I am trying to integrating Drupal with Mailchimp.
I have following queries regarding the same.

1] In "List and User" option, when I select "Required" option it will gives us a checkbox for
"Enable MailChimp webhooks for this list ". I have ticked and checked this option, but when I unsubscribe any email it will enter that email data into "cache_mailchimp_user" table.
But what is the use of that table. What’s the purpose in Drupal. How do I use this information?.
2] when I was creating a campaign via drupal it will created in draft mode. How can I send campaign using Drupal, also how do I check the reports of campaigns In Drupal.
3] In "List and User" option, when I select "Optional" there are check boxes "Include interest groups on subscription form." what does it mean. What happen when I select this option?