On an s-trim, I wouldn't like that. it's recomended that 8psi and above should use a bypass, plus it's open at idle so the air is not forced into the TB cause the blower still blows a lot of air at idle...
I'm running 6psi on an A-trim, and I think it's causing some drivability problems, like surging idle, etc....I don't have the bypass on mine because i don't have a vortech discharge but am supposed to get one from someone I know soon....i have a upgraded bosch bypass...but like i said it's not in, but I wish it was!
I was pushing 9-11 lbs and my car wouldn't idle for crap...it would actually die when stopped if I didn't hold the gas. I guess it COULD have been other things, but I think others have had the same type of thing w/o a bypass. I'd just put one on so you're safe, however I also have read that w/ 6 lbs or under, a bypass isn't needed, so...I guess this post really didn't help much huh?