The most common use case is modifying an effect’s parameters at runtime. How it works is practically identical to Unity’s own effects can be modified, the difference being the effect you want to address.
Built-in Render Pipeline (Post Processing package)
The package’s manual has a dedicated section regarding this.
Universal Render Pipeline
The concept is the same, yet the syntax differs slightly.
I’ve composed an example script, which jolts the intensity of the Radial Blur effect quickly up and down when you press the Space bar.