When is Sure-Grip actually necessary?

With smooth pavement, dry conditions, good tires, and 300 HP with the likely torque you will have, you will do Ok without it. It will just spin a bit and go at worst in those conditions, if you learn to manage it (not hard to learn). What is your need in the car? Regular driving or on the strip? And BTW under snowy or loose gravelly conditions, a really tight posi will help you get going but can be a detriment in turning.