If the standard brake lines are old,worn or understrength for the hydraulic system, when you press the brake or clutch pedal force that should only go to operating the hydraulic device is reduced because some is spent making the line expand. This is generally not an issue on street cars. If your lines are old good, high-quality hydraulic line should be more than enough.
If you upgrade the brakes and need clamping power that is at the edge of what the stock hydraulic system can provide, they can help bridge the gap while you solve the real problem and increase hydraulic pressure.
If you upgrade the hydraulics beyond what the stock hose can handle you can just upgrade to better hydraulic line; SS is not needed.
It does look cool, which is probably why most folks with street cars do it. Nothing wrong with that, though it does have a strong placebo effect given the prices paid through auto after-market stores (hint, look in your phone book under hydraulics and you'll probably find a hose maker who can save you bucks).
Keep in mind that you will want to be careful when routing the SS hose and keep it away from all of the usually softer hoses and lines it tends to run near. It's strong and hard stuff and will slowly tear up softer lines.
As with replacing any hydraulic line it's a good idea to do a bleed. It's only a little time with a Mity-vac and it never hurts to get fresh hydraulic fluid into the car.
-Rich
Whats the benefit of the braided line, better clutch feel?[/b]