I believe this means the seat slightly adjusts itself over time, side-to-side, to prevent pressure points from developing.

Back in the 1960s, GM while testing vehicles coast-to-coast tried to find which seat type was most comfortable. What they found was that after a while, many of the long-distance testers would sit on their clipboards, simply to get a different set of pressure points on their posterior.

It's the same concept as why people get bedsores when they are bedridden.

So the active seats simple adjust the postion subtly over time to avoid developing pressure points.

I'm 95% sure about that explanation.