Should I use RayTracingShader or CommandBuffer for RTX feature?

I am learning writing my own ray tracing shaders in Unity. I found two classes can do almost the exact same things for RTX:
1. RayTracingShader (https://docs.unity3d.com/ScriptReference/Experimental.Rendering.RayTracingShader.html); and
2. CommandBuffer (https://docs.unity3d.com/ScriptReference/Rendering.CommandBuffer.html).

Every method in RayTracingShader class has a corresponding method in CommandBuffer class. For example:
* RayTracingShader.Dispacth => CommandBuffer.DispatchRays
* RayTracingShader.SetAccelerationStructure => CommandBuffer.SetRayTracingAccelerationStructure
* RayTracingShader.SetTexture => CommandBuffer.SetRayTracingTextureParam
...

So, what is the difference between using RayTracingShader and using CommandBuffer? Which one should I use? Why does Unity have two ways to do the same thing? Or are they for different purposes?

 

Anybody with RTX experience can help on this? Thanks!