It really depends on what kind of driver you are and what car you are driving.
If you are comfortable and consistent with throttle control even at long races , then just turn it completely off. It's going to be an unnesssesary handicap anyways.
HOWEVER if you do mistakes frequently (losing it mid-corner , spinning while exiting etc.) it would be better using at least tcs 1 , or even 2 since the car will still be spin-prone even with 1 setting. It's better to be slow but consistent than being fast but risking a spin every corner , the extra tenths with TCS off in that regard aren't worth the risk imo.
Additionaly , it also comes down to the type of car. TCS 1 or 0 is just fine for Gr.3 cars , while in Gr.2 i prefer using TCS 2 , they are just too twichy to control otherwise. Gr.1 is the same with Gr.3 , since they are much more stable.