Thumb rests help you to achieve better shooting results. How? Through better recoil handling as you will have a better grip of your handgun.
By pushing the gun downward with the thumb rest, you will be able to handle it better.
Types of thumb rests
There are few types of thumb rests.
Some are only to be attached to the frame mounts, and thus accomodate your left thumb in the front of the handgun.
Another type of thumb rests are positioned above the trigger guard, and are supposed to accomodate your right hand thumb.
You can find such as a part that comes together with slide stop, but also as a separate part that shall be installed as a replacement of factory thumb rest [that is for CZ TS 2 models with factory thumb rest custs in the frame].
You can also install a thumb rest into any other position on your gun, but then you will need to drill into the frame.
Thumb rests for competitive shooting
The main reason for a thumb rest is to achieve better shooting results by having more control of your gun.
The thumb rest that is installed to frame mount allows you to have even more control as the thumb rests is for left hand thumb, giving you the option to push the front of the handgun lower and fight the recoil.
The rear thumb rest gives you less leverage over the recoil, but it still improves your recoil handling considerably.