Why are server-to-server traffic flows routed through the aggregation layer?

Why are server-to-server traffic flows routed through the aggregation layer?

A.
They are routed to provide increased fault-tolerance and smaller STP domains.

B.
They are routed to provide load-balancing services between web and application servers.

C.
They are routed because individual access modules cannot scale to large HPC deployments.

D.
Server-to-server traffic flows should never be routed through the aggregation layer.