When do you need to build?

Hmm… but is the Building the Baking? I am confused, because I have in my PostProcess Volume and the Project Settings Raytracing turned on.
I raytrace GI, Reflections, Shadows and Translucency.

When I do so… isn’t that happening in realtime automatically?
Why would I need to click build?

Thanks for helping a bloody rookie understanding this process!
Appreciate it!