Connect domain auto-renewal with registrar options
Currently this option only relates to if the renewal invoice will be issued or not: https://docs.whmcs.com/Domains_Configuration#Automatic_Renewal
Registrars often have their own auto-renewal settings which (if turned ON) will renew the domain regardless of the payment status in WHMCS. In majority of cases it's useless or even harmful to use it since all renewals are triggered on payment in WHMCS.
There are ccTLDs that need it enabled to renew properly (at least at Enom) but we've build a system to turn it ON when a ccTLD is paid on WHMCS end, and turn it OFF again after the renewal is complete.
We keep this setting turned off with our registrar by default to minimize the risk of domains renewing without us receiving the payment first. There are some cases though where auto-renewal was turned ON and wasn't turned OFF on registrar's end (human mistakes mainly).
This could serve as a second line of defense, disabling auto renewal in WHCMS could make sure it's disabled on registar's end too.