The automatic renewal means you will be billed for your access to the software on a monthly or annual basis, i.e. your credit card will be charged every month or every year automatically.
After the expiration date of your subscription the system will automatically renew it for another billing period (month or year).
This is an option that can be enabled/disabled at any time for any term license before its expiration date through my.chaosgroup.com
The pros here is that it saves you time and effort by not having to make new purchase every month/year and also ensures your work is uninterrupted.