WHM Spellspeed! Any value?

[KahnMeido]

To give an example to elaborate the above, imagine two situations:
1) Tank about to die, cast heal, slower by 0.1 seconds, tank dies, if only I have faster casting speed!!
2) Tank have 1k hp, you cast heal, you manage to heal the tank for 1300, but boss attacks for 2310, so tank still dies, if only I have slightly more healing power!!

or situation 3 where you were already precasting so it doesn't matter. .1s spellspeed =/= already being halfway through a cast when the damage happends.