talkin about starting at 2. its good if you dont wanna burn out tire, it gives you more traction as it takes acceleration power. this is good on slippery road or if you just wanna accelerate slow while driving somewhere cautiously while you have ur foot on the pedal.
as for shifting by itself, i really have no idea cz i never driven a sportshift gts.
as of downshifting, i dont think its a good idea if you cant rev match, and i dont think you really can rev match on a sportshift. first of all, when ppl say that rev matching is better than braking and stopping cz it saves brake pads, thats kinda bs. ur not eating brake pads, but ur burning gas like crazy, and putting pressure on the engine all of a sudden especially if you downshifted and revmatched at a high rev. i think thats more harmful than brake pads or brake rotors. but it is useful somtimes to downshift and revmatch, and brake at the same time cz im sure itll get you stopping quicker and easier.