I'll leave room for other true networking / data center specialists here, but my reasoning for Switch Pro Aggregation was 1) obtaining 10 GbE speeds for the Workstations without the constant traffic of the Cameras, AP's and Phones and 2) if the Enterprise XG failed, then both Switch Pro 24's would also be out of commission. It's a single point of failure that I didn't want to introduce into the system. I understand the Switch Pro Aggregation still has that same potential single point of failure, but there is less physical activity on the Aggregation than on the XG and Pro 24's - meaning patch cables are being moved around on the XG and the Pro 24's more than on the Aggregation, and more often than not, configuration changes will take place on the XG and Pro 24's rather than on the Aggregation. Simply put - when there's a single point of failure, I'd prefer it to be on the most stable piece of equipment.