Couldn't impeding the string even in the least change the characteristics including the speed? I am not sure about this but doesn't the arrow remain with the string upon release until the string finds its final forward motion?
Yes, which is -- as Len pointed out -- one of the positives. This stopping the string at brace prohibits the string from impeding the arrow's speed by "clinging" on to the arrow nock as it begins to slow down past brace... Some people have experienced a 3-4 fps gain just by using an STS.
But, it appears Buck Magnet has discovered a negative which may outweigh that positive... and the noise suppression abilities as well. I wonder what the guys in Dyersburg have to say about it...