It's not required to get into melee range, but if you want to play the job with the easiest flow and simplicity, you use Corps-a-Corps to get into melee range and Displacement to get back out enabling you to use the maximum amount of time casting. You don't clip time you could be doing DPS by moving. As such, if your spell speed is too high, then you can't utilize these skills. Optimally you want your spell speed to enable you to be at 80/80 mana every time Corps-a-Corps comes off cooldown, and no higher.
