Obviously if you like the look of a render then its useful :) But there is nothing in Superfly that prevent you from achieving a certain style, it doesn't have to be "realistic", which it seems to be referred to. But when you talk about realism in regard to PBR its about how it handles light and not so much about the look of the image, where you in Firefly have to fake it. I agree that you can get some good renders out of it, if you take your time. But being able to make materials and knowing that regardless of light settings, that being night, day, red light, blue light etc. It will look correct. Where as you in Firefly can risk that a scene looks very good with some lighting, then you change it and everything suddenly starts to look wrong, so what you have to do is start tweaking and adjusting all thoughts of things to make it look correct. PBR due to how it works solves all that for you, which is a huge time saver. Also you can take any PBR textures and throw them into another PBR and it will look almost identical with very little work, depending on the engine, so suddenly you get a lot of flexibility with your assets.

But there is nothing in Superfly, that prevent you from making some cartoon textures and throwing them on your character, the important thing is how it handles light and that you never get more than you throw in, and at least in my opinion, its doesn't really matter what style you are after, unless your aim is something like that obviously, the better the lighting the more interesting your image is. You have to remember that colors are simply reflections of light, so if the light is bad or wrong it will affect the image. And as computers get faster and faster so will rendering be. And I myself don't have a fast computer either, but I would imagine that people that have fast ones Superfly is godsend for Poser.