Front stabilizer bar?
 

Why do some people take them off for the track?

It takes weight off the front end but the main reason is that it allows your front suspension to expand quicker and throw the front of the car in the air to help the weight transfer to the rear. A lot of people do it. But i wouldnt recommend driving it on the street for to long like that.

Ok, I see now. Now is it really that bad for DD use? I read that some people DD with it off and barely can tell its off? I used to DD jeeps all the time w/o sway bars and could barely tell a difference, but im not sure with mustangs.

The stiffer your springs are the less youll notice. But youll notice the front end will seem a lot more likely to dive during spirited turning. Youll get a lot more body roll. You could take it off and try it without a little bit, but youll need to slow down a little on some turns that you might not otherwise have to with a front sway bar installed.

Yeah so I took it off because I was bored in the shop today and the front end picks up a ton more and has quite a bit of body roll. I'm gona test it out for a day or so and see what I think. I could use some stiffer lowering springs but dont want to have to buy all that extra camber plates, struts, shocks, bumpsteer and what not.

I always leave mine on till i get to the track and just undo the endlinks and let the sway bar hang.