[nbm]

Even in the proxy case (which is my day job), it's often worth the price of the up-front load polling to have sufficiently recent information to take action on. The most obvious cases are those where you have some (or all) requests being expensive, as opposed to thousands of exclusively tiny requests.

This does depend on having a local load balancing layer (not, say, making a choice between two servers that are each 50+ms away from the load balancer), and also having a high-performance RPC stack (C++ on both sides, and Thrift, in my case).