I don't use any aids if I can help it. I sometimes forget and then get frustrated that TCS is sapping my exit speed, but the ABS in GT5 is a great improvement over GT5

and GT4.
For some licence tests and special events, I keep ABS on, especially if I can't adjust the bias in time via the in-race menu. Not sure if it's an advantage or not.
I think people should do as they want with their game, but the point made earlier about the racing line is valid. Learn to read the circuit and memorise it; eyes up, spying where you want to be next (this works with so many other sports, too.) That's the key to improving in general, because you're automatically more aware of where you are and what you're doing with the car.
I like the feel of the cars with ABS off, so I drive with it off whenever possible, irrespective of whether the car has it or not, and adjust the (frustrating default) bias to suit. 👍
If I switch to the pad for grinding, it can catch me out, but I usually can't be bothered to change the settings on my work horses, so I just drive a bit slower
