idea
When programming buttons, acting on release is introducing a noticeable latency, and UI seems more sluggish. Acting on press is better to make things seem more reactive and real-time.
However acting on press prevents the pattern where you can move your finger or pointer away from the button to cancel the event. This can be compensated by adding good cancelation logic, or confirmation dialogs.
links
references
John Carmack on Twitter: Act on press