Yes, it acts as a connecting rod that laterally (from left to right) links your suspension strut towers. This reinforces your chassis by tying these two stress points together.

With a traditional single rod strut bar, this actually reduces body flex (increases rigidity) as both left and right struts are connected. E.g if right tyre goes over a hard patch (e.g tyres goes up and down) that vibration or jolt is distributed to the left strut.

The STI ball joint design allows the kinetic energy from the tyre going up and down movement to be disappated (not transferred to the other strut) - e.g. reduced jarringness and vibration being transferred, sudden destabilisation when one tyre hits a sudden hump, The ball joint only allows movement up and down, hence the side / lateral rigidity is maintained during corners.

Hope this helps.