Its supposed to give a % extra to turn rate the more aux you have. Problem with the Galaxy and Sovvie are that their base rates are so low that that bonus isn't really noticeable. Something about 20% of 5 is still 1, ie 6 total.
I've plenty of power, and don't mind adding to Aux, but if the difference between 100% and 0% is not significant (i.e. I can't measure it at all in game), it's pointless. If I "transfer all power to the lateral thrusters", I want to TURN!!! I don't want to fly faster, I want to turn faster.
And they can't quote inertia to me because I can go from 0 to full impulse in seconds and slam into another ship with ramming speed, going from 0 to 100% and then to 0 in seconds without turning my crew into goo on the walls, so I should be able to do similar things turning.