Depends on what kind of effect you want to achieve really. If it is a post effect which you cant create with a post process volume’s properties then you’ll have to use a material.
If it is localized as in you see the effect when you are in another post process volume then fine, you dont need a material. But i just checked the blog post you linked in the first post and a post process material is definitely needed for that kind of localization.
That’s a pretty cool idea actually. Just make it and see if it causes any major frame rate drop. You can also use GPU profiler to see exactly what kind of an impact such an effect would have. Dont be afraid of PP materials, btw. They dont kill the performance so easily unless your material is something crazy and has a couple of hundred instructions.