I wrote this on another topic, and thought I'd write it here too, because it definitely affects GCD usage and such:

Square said they didn't want to stress servers and only make a checkup on your location every 0.3 seconds. It will end up not working in the long term.

Make a boss ability where the delay between the visual for the spell effect and the time we have to move is 1.5 seconds. Now, consider the AoE appeared 0.3 seconds later than it really got cast, consider the 0.3 seconds server checkup on our location. You have 0.6 seconds less to move. So a 1.5 seconds time reaction is going down to a 0.9 seconds reaction time.