The primary benefit to rendering the HTML on the first request (as opposed to a subsequent request through AJAX etc.) is that you don't have to wait for another

The primary benefit to rendering the HTML on the first request (as opposed to a subsequent request through AJAX etc.) is that you don't have to wait for another round trip of latency. Note that this is not improved by additional CPU speed, and even additional bandwidth will not completely eliminate this bottleneck. As I understand it, Twitter tried full client-side rendering for a while and went back to a progressive enhancement model, because they noticed that an extra round trip of latency is enough additional load time to be noticed by the user. HTTP/2 will shrink the benefit of first-load rendering further, but it's currently still an important consideration to make if load time is a primary concern.