negative camber increases grip during cornering. go too far though and you lose stright line grip so compromise acceleration andbraking. this is only going to be seen in track cars that have a LOT of adjustibility though and even then most track prepped production cars are not really gonna see it, only the likes of btcc cars and proper racers. have you seen how much negative camber the btcc boys run? fucking loads!!!

on a mk1 focus lowered 30mm you shouldn't even need the bolts tbh. if your on oe bushes that are old and a bit slack though that may add more neg camber but not much. i'd only upgrade to adjustible stuff if after a 4 wheel alignment (which should be done after lowering) you get excessive inner tyre wear.