Too fast on the trigger is as bad as too slow.
Here’s a fun one. It’s possible to be too fast on the trigger for your own good.
Let’s set up a simple pattern recycling: (MB-MF-MF) x3(MB)
That’s three cycles of MB-MF-MF (9 casts) ended with a mindblast. That’s notionally 12 seconds of casting. We’re going to use my nominal damage values of 1450 for a full mindflay and 1540 for the mindblast.
We’ve got two shadowpriests. One’s a little slow on the trigger, with a definite (about a tenth of a second) delay between the end of one cast and the beginning of the next. The other tries to hit the button exactly on the end of the first, even going so far as to use a lag compensation tool. Who, over an extended fight will do the most damage (and so the most dps)?
The slow trigger.
Here’s what happens. The slow trigger gets everything from his spell sequence. Which means that although the total time for his sequence is 12 seconds of casting plus 0.9 of lag for a total of 12.9 seconds, he’s getting 14,860 damage for a dps rate of 1151.9.
Our fast trigger is interrupting the mindflay about half the time and not getting the last tick. Consequently he’s still getting the 8700 from four mindblasts, but half of his mindflays are only getting two ticks off for roughly 967 damage. So the total damage is (3*967)+(3*1450)+(4*1540)= 13,411 damage with a dps of 1117.6.
The moral is that while you want to minimize the gap between when one spell is off and the next begins, you have to watch out for the overlap, because MF procs exactly on the full second. Too early an interrupt — no damage.