The overhead is only the latency of the ajax call on the first load (since you are going to the server to fetch the app code, then going to the server again to

The overhead is only the latency of the ajax call on the first load (since you are going to the server to fetch the app code, then going to the server again to fetch the data, instead of going to the server and fetching the app code + the data). For every consequent page transition the performance is actually slightly higher than a full page load since (a) you're probably only fetching JSON instead the entire resulting rendered HTML and (b) you don't have to load the app code any more.