A Strut Tower Brace has also often been called a Strut Tower Bar or most often simply a "Strut Brace". The Struts that are being braced are typically the front upper mounting points for the assembly of the springs and shock (Strut Tower). This strut carries the main load of the suspension and maintaining exact control of their location in cornering can mean the difference between a performance handling car and a so-so driver!
Reducing the flex in these towers will help control caster and camber. This will improve traction on the turns and better turn-in response and could actually reduce understeer.Take a good look at any strut bar and remember that its primary function is to control flex, it is not to simply look shiny and cool. The bar must be designed to not flex and thus must be as straight as possible, and it must take all the horizontal loads without bending or distorting. A bar that pivots at the mounting points is just cosmetic and cannot do the job of keeping the suspension geometry in place.
A solid brace will keep everything in place and allow the suspension to work as designed not only when the car is new but will add greatly as it gets older and older. Installation on a new car will keep the car feeling new for a long time, while installation on a used car will almost make it feel new again. Not only does the strut brace give the car structural rigidity, but the car is far less likely to have the classic squeaks and groans of old age.
This is one of those upgrades that would be considered not just for the racers or occasional track day participant but for the daily driver. A sound handling car is a safe car in the hands of someone that cares.