Just for original reference here’s the unfiltered vs filtered version of the OP.
I modeled this in gravity sketch (exports crude .obj files), rendered in keyshot, added noise and chromatic aberration in Ps, and finally a instagram filter and adjustments.
The main reason I add the post-processing is for realism. Google “how to make a render look realistic” and you’ll get all kinds of tips and tricks on how to add imperfections to achieve a more photorealistic render.
I always thought that this was only in student renderings done at the last minute! Seems like a trend now.
One place where I have seen noise work is in depth of field. DOF can add some drama to a render, a little more realism and some grainy artifacts that look like a photo and not a render.
I spent sometime in the film vfx world before moving into ID. This trend may be new to the ID world, but it’s a common technique used by 3D film compositors. It’s used to match 3D to film plates during post production. The reasoning being 3D renders often come out looking to perfect and clear compared to the film footage which often has sometime of grain associated with it. Another trick was to use an edge mask to slightly blur the edge of 3D assets to break up super sharp pixel transitions with film footage.
Every photo-realistic render should have some type of grain, as many other’s have said in this thread we are simulating a camera photo. That being said it should be used with a reason. Close up or detail shots on small and even large products should include noise along with DOF. In context product shots should also include a small amount of noise to match the photo background. Pretty much any other type of product shot can include less than .75% noise to just break up that perfect render look. This all being said it’s a stylistic choice for many designers but these are the rules of thumb I was taught as a VFX artist.