Separate NFB from driver

Looking at a service manual for an old subwoofer design by Kenwood which has emblazoned "sigma servo" on front to see what exactly they were on about. I've heard of servo woofers but not in the low end consumer market.

Anyway what I found was they were running a separate feed from the + terminal of the woofer for NFB. Which makes me think it is no more than just a bit of a gimmick for marketing purposes.

However it got me to thinking. Has anyone experimented with this arrangement and what effect did it have? Or otherwise have thoughts on the matter? It seems that it would be an opportunity to at least partially null out the effect of speaker cables but I can see it introducing a new set of problems (it may need to be shielded for longer runs, etc and the return would introduce its own distortion).