the struts induce higher loads than the spring from my understanding, but I'm not 100 percent on that
vince posted the long debate from corner carvers which makes for an interesting read if you haven't before
Basically in theory the stb actually keeps the strut towers from moving apart from each other in cornering, maintaining alignment which is determined by the movement of the struts on a macpherson car
the other arguement is that it also helps distribute loads from bumps. This is debatable because the strut towers are one of the stronger points on the unibody
I honestly don't know if it made a difference, I'm still rocking stock suspension and I could barely tell a difference when I put on my MM full length subframe connectors, it just felt a little better over bumps imo, I though turn in was slightly better with the stb, but that could just be my mind playing with me because if I spent money the car MUST be better right?
It couldn't really hurt imo, and the verts need all the damn bracing they can get