is that where you set the drive to 0?
which is good for the metal tightening up purpose?
Pretty much, yes, but the effect will still happen regardless of the amount of drive you have on the pedal.
OD pedals have a bass filter that cuts frequencies below a certain point, leaving you with a far tighter sound. Tubescreamers are often used as their mid hump adds extra cut and grind to the sound, which can result in much chuggier palm mutes and can help you punch through a band mix a little better.
A regular poster on the SevenString forums mods and builds pedals. He makes pedals with the metal player in mind, and from all reports his pedals sound brilliant. As soon as I pay off my Blackmachine, I'll be getting myself one of his "Bloody Murder" overdrives (don't worry, you can have it named and painted whatever you'd like!), which is essentially a TS clone, built up from scratch with lowest tolerance parts, designed specifically for metal players.
His stuff is very well priced, especially taking into account the exchange rate at the moment. (shipping to the UK is $10 btw)
His website can be found here:
Bodenhamer Electronics