up or downside is 3gbs bandwidth. If there is a 6gbs interface available and you don't have a drive capable of taking advantage of the extra bandwidth afforded by sata III, that's your choice. If 6gbs is not available on the machine, its not your choice. You can spring for the fastest ssd on the market and still top end at 3gbs. Setting aside the possibility of any express card fed external raid units. Having or not having sata III would count for a lot.