It may not reduce que time but it increases the total of flashpoints formed. Take for example the folllowing and more realistic situation...
Server A: 3 tanks, 1 healers, 8 DPS
Without cross server, this server can create 1 FLASHPOINTS
Server B: 0 tanks, 2 healer, 3 DPS
Without cross server, this server can create 0 FLASHPOINTS
Server C: 1 tank, 2 healers, 5 DPS
Without cross server, this server can create 1 FLASHPOINTS
(2 active flashpoints)
In total, we have 4 tanks, 5 healers, 16 DPS.
With cross server, you get 4 flashpoints up from 2.