What these brackets are designed to do is bring the line of action of the trailing arms back pointing towards the centre of gravity of the car. The problem with lowering a car is that while you are lowering the centre of gravity a couple of inches, you are making big changes to the effective geometry of the suspension. These brackets are supposed to restore some of the geometry after you lower it.
I keep telling people that when you lower a car you stuff up it's handling and they keep telling me that I know nothing. My car was lowered before I got it and it's handling sucks. It has all the big sway bars, stiff springs and hard shocks that "should" make it handle.
Anyhow, enough of my car. The point is that these brackets are supposed to install whats known as anti-squat. They are designed to line up the thrust line of the tyres with the cars centre of gravity, thus getting the most bite from your tyres.