It improved both mechanical and aero grip at the same time, but the primary purpose, as per Toyota's senior chassis engineer, was to be able to stabilize the aero platform, specifically around pitch. Which makes sense: same reason active suspension came into being, even at the expensive of grip. Aero gains are more productive, on balance, than mechanical grip gains, at least in Formula 1.

It was moveable ballast, plain and simple. In its early guise, was totally unconnected from the suspension. So that's a pretty easy distinction to make vs. springs/dampers/anti-roll bars.