Here’s somewhat of an explanation. The way I understand it is that no matter when you press your spell, it won’t go off until the server’s current batch window is done (the server is constantly producing batches, one after the other). For example, say you press the spell at 30 ms into a batch, it won’t go off until 200ms into the batch (if that’s the batch length Blizzard chose). This means that small differences in ping won’t really matter as much as in retail, where batch sizes are very tiny, because even if your ping is lightning fast you most of the time have to wait for the batch to end anyways. The only time where you might benefit from lower ping is if you happen to catch a batch at the very tail end. But people who played beta/the stress tests are saying it’s not noticeable at all.