Personally, I turn off all the assists that would otherwise never have been in the specific car I am driving. For instance, if I'm driving a pre-'70s production model car, I doubt they'd have had Traction Control or ABS as standard equipment, so I turn those off.
On the other hand, when I started out the game and wanted to gain quick wins, I didn't disable anything that helped me do so. The previous paragraph only applies to my current gaming, not what I did at the start.
It all depends on your specific goal and specific car at the specific time, and each car has the potential to behave extremely different on each different track, making it almost a requirement to check and/or change those settings before each run.