What does the advanced section do?

Most users will not need the advanced section, so it is collapsed and hidden from view.  When expanded you will see three options which are described below - 

• Update Lead/Contact Email Opt Out - Enable this to use the opt out feature.
• ‍Enable Debug Logging - If you encounter a problem, we may request access to help.  At that time if the issue is not clear, we would look to enable this option.  Once enabled, our support team will see additional information in our logs.  
• Archive Mailchimp Member on Delete - Enabling this will automatically archive correcsponding members when you delete an account, contact or lead. (User deleting records must have one of our permission sets).
• ‍Disable Salesforce account, contact, and lead triggers (Salesforce to Mailchimp edits) - Enabling this option will stop our triggers from firing when you edit an account, contact or lead. The trigger is designed to update Mailchimp should an email address on a single record be changed or if you have field mappings in place. If you want to stop this behavior or are having issues with triggers in general, you can enable this option.    
• ‍Disable bulk triggers for account, contact and lead triggers -  This works like point 2 above.  The only difference is it refers to bulk actions.  Bulk means when multiple records are updated at the same time.  

Note that email updates can't be performed in bulk (see email updates).