Jaco: RISC OS isn't very responsive to clicks when, for example, you're doing a file copy (especially if it's 'faster'). PMT would allow file copies to run at 'faster' speed until the millisecond you make a click, at which time the copy will temporarily pause to handle your request. You could even acheive full display updates at almost 'faster' speed, as you'd be able to update the display without all the other apps grabbing a slice of time needlessly.
Drags are faster because as soon as you start a drag, RISC OS actually stops multitasking and becomes a single-tasking OS, for example, stopping any servers you might have running. That's the case for window drags at least, I think. Not sure about file drags - I suspect the graphic is done via MOUSEV.
Meanwhile, Ethernet events actually require even faster responses than you or I. Just because it looks instant to us doesn't mean it's fast enough for a network.