For all those who still have doubts about multithreaded ajax, I built an example that illustrates the differences between ordered and unordered batches, as well as synchronous and asynchronous.
Ordered batches will force the batch length to remain at (1) at all times, waiting for a response to come back before sending the next call.
Synchronous batches will halt the batch until the callback function has been resolved, making the entire process single threaded.
Note that the synchronous process will take a few seconds… this process in not meant to be used like this, but I wanted to illustrate the consequences. There are extremely handy uses of the synchronous process, which I'll show in a different example.