A strut bar is designed to reduce this strut tower flex by tying two parallel strut towers together. This transmits the load of each strut tower during cornering via tension and compression of the strut bar which shares the load between both towers and reduces chassis flex.
So what does that mean for your WRX? Here are some personal opinions of mine on the FRONT strut brace on my 2000 Subaru WRX (GC8):
Cusco Type OS (Type2) Aluminium Front Strut Brace
Sharper turn in
Without a doubt the first thing I notice when using the front strut brace just how sharper the turn in is. There is no delay or 'give' when you yank the wheel around a sharp corner anymore. I recently had to take my strut brace off for a few weeks and I used the oppoutunity to feel how the car handled without it. There was a definate lack of feedback with the turning. The front end would wobble around and it felt like the struts were soft like on a really hot day. As soon as the front strut brace was reinstalled, there was an obvious sharpness and stability to the front end again.
Better front end balance through corners
After the initial turn in, while holding the corner, the front end appears to be much more stable, you don't need to make adjustments to the wheel to keep the balance, it just keeps the weight well shifted. Much more feedback from the road, which translates into a bit more feedback through the wheel, but in my opinion this is exactly what I want.
Increased grip, resulting in reduced understeer
Because the strut isn't moving around with the flexing of the chassis, the contact patch between your tyre and the ground is increased. This means you've got more grip under load and this will result in less understeer - perfect for an understeering car like a WRX.
I hope this post was useful to those starting to look at mods for the WRX. I also have a rear strut brace which does pretty much the same thing on the rear - Better handles the weight shift at the rear of the chassis.