I guess it depends on the car. Ive done research on chassis strenthening for my car. Depending on who makes the stuff the claim
it does "this" and "that." Best thing to do is talk to people who have used the stuff that know when a chassis is flexing or not.
I've heard that a chassis is weak at the firewall. Ive seen triangular braces that bolt behind the fenders like these that aid in that.
Those style strut tower bars may do something similar. I run no chassis strengthening and dont seem to have problem with it. I see strut tower bars, as probably beneficial, but more of a part people seem to think they need b/c they see other people with them on their cars.
Chassis bracing is kind of ambiguous. People dont actively test or prove alot of it. I dont see alot of public tech. information out there either. At best you get "My car FEELS stiffer now." Unless someone put a chassis on a machine that actively twists and flexes it Im not sure if there is any real proof out there. If there is please forward it to me.
Any time something is triangulated it will be stronger. But its hard to know what the exact dynamics of the chassis under stress. I would think that the ones that bolt to the firewall will add more support.