I'm going through the documentation in databricks for using existing VPC requirements. For the section that covers ACLs, what's the need to have this inbound rule: " ALLOW ALL from Source 0.0.0.0/0. This rule must be prioritized."

https://docs.databricks.com/en/security/network/classic/customer-managed-vpc.html#id7 

can someone explain why this rule is needed, what is the use, and what's the alternative if we want to have a more restrictive rule?