When a VPN is established between the data center and the SDDC Instance, it allows the organization to create a private and secure connection between their on-premises infrastructure and their workloads running in the cloud. By advertising a 0.0.0.0/0 route, the organization is essentially routing all traffic to the VPN tunnel, which means that all traffic including traffic destined for the data center and internet traffic, will be sent through the VPN tunnel to the company's data center.

It is important to note that this configuration depends on the company's network architecture and security policies, and that there may be other alternatives that better fit the organization's needs.