Hi, I speak for the classic WoW speedrunning community, and we often use the batching mechanics to hearth somewhere while setting the hearthstone to the previous location.
I will explain with detail: You run up to the innkeeper, open the hearthstone bind location prompt, start casting your hearthstone and then click accept when the spell cast is almost done.
This allow you to, for instance, hearth from Darkshore to Westfall while setting your hearthstone to Darkshore, so you can level faster by using your hearthstone to travel between Kalimdor and Eastern Kingdoms.
With the reduction of the batching window, this is still possible but instead of having a 400ms window to pull that off, you now have a much shorter window, and if you consider things like latency jitter, what used to be a very consistent trick to pull off, is now pretty much random.
If you look at this through the lens of a speedrunner, that means you have a random chance of losing your run to some arbitrary random mechanic outside your control, which only sucks the fun out of speedrunning the game.
I did some testing on the PTR and found out that changing your HS bind location is still on the 400ms batch window while the 10s Hearthstone cast is not.