True, you get a looser car, which nets more steering, from moving the hubs back. You also get more stability in the rear, but only about 3/32(3mm?) of an inch worth or so.
Since the center of mass doesn't move, but the rear tires get moved farther away from it, you'll have less rear traction and more steering under power, with slightly less off power.
My lap times got slower when I moved the rear hubs on the two Florida tracks I tried it on. I tried it, since so many factory guys run that setting, but for me the added wheel spin and excess rotation(from the rear) hurt my lap times. Basically, since my car had good steering already, freeing up the back wasn't helpfull. But if someone is on a track that gives a push, it may be the way to go.
For example, the new version of the 777 (SP2) has the motor moved back to gain traction since they found they had overdone the "freeing" the car up design. This leaves the wheelbase where they want but improves the balance.
When I ran a Crono RS01, several years ago, I had custom engine mounts made to make the motor position adjustable....
, Jim