The automatic renewal means you will be billed for your access to the software on a monthly / annual basis, or every 3 years, i.e. your credit card will be charged every month / every year, or every 3 years automatically.
After the expiration date of your subscription the system will automatically renew it for another billing period (month / year / 3 years).
This is an option that can be enabled or disabled at any time for any term license before its expiration date through my.chaos.com
The pros here are that it saves you time and effort by not having to make а new purchase every month/year/3 years and also ensures your work is uninterrupted.