Personally, I am not a hard core sim grinder like some of my pals, but those that are dedicated to the point of stacking hours and hours training their brain with the use of sims swear by these little thumb protectors.
As I understand it the benefits are twofold- First off it protects your thumbs from getting eaten up by sharp stick ends after hours of deep grind, but secondly it gives your thumbs additional grip.
This is an add on product, meaning it's free if you're buying other stuff! Max is two (one per thumb) per order. Feel free to get a set with each order!