for healers alacrity is important. that heal going off a half second earlier is the difference between a successful boss fight and a wipe. even if youre waiting for the 1.5 global cooldown your heals are still hitting faster, and suppose you only need to heal someone once? same deal. either they get healed, or they die.
also, (for ANY class) there are abilities that are longer than 1.5 seconds. lots of them. lots and lots of them. not having to wait as long for them can really help. but mostly, its a healer stat.
lastly! @Gariuys... as stated above, your not noticing the .1 second delay. either its latency, or input lag or an aspect of the mind not noticing a tiny tiny delay like that. if you really wanna test it. set a timer on your phone or something for 15 seconds. you should, in that time, be able to get off 16 power shots/missiles/grav rounds. i promise that in the time youll only see 15..... ammo/heat should last through that spam right? even if your target does not...