[pas]

Usually both properties are desirable .. up to a point.

You want to minimize load on all servers, but you also want to pack things up efficiently (so minimize operational costs), but of course you want the benefits of caching, so you want requests from a sessions to land on the same node/server/box.

Basically a multi-dimensional optimization problem. Completely solvable with constraints. Let the business people decide what's more important, latency or throughput or low cost of operations.