There is a need to ensure that all traffic stays within a specific geographic region or a specific data center.
With explicit proxy, you would add a new PAC file in your portal account that specifies a specifc data center (using its IP address) instead of directing traffic to proxy.threatpulse.net as the default PAC file does. You can add multiple IPs to add redundancy. Ideally, you would want to list data centers that are closest to reduce latency.
Please reference the following article for a list of data centers and thier IPs that can be selected based on your needs:
Data center IP addresses for Web Security Service
Below are the steps to add a new PAC file with specific data center IPs listed:
A note on locations:
If all your locations are relatively close geographically, you can use the same PAC file to direct all traffic to the same data center for all locations. For example, if your primary location is nearer to one data center, but you also have another location closer to another data center, you may want to create and use a different PAC file for each location with the closest data center listed as the primary data center in each location's PAC file to reduce latency.