Nearly every post-processing effect can, if used correctly, improve the graphics of a game.
>chromatic aberration
If used sparingly, in certain situations, it looks good. Like how in Crysis it only activates when your suit feels power fluctuations or alien signatures nearby. It's a good active effect. Of course if a game just passively aberrates everything nonstop then yeah turn that shit off.
>film grain
Certain games have an artstyle or textures that can result in a plasticky look that lacks grit. Film grain can offset this in the correct amounts.
>motion blur
Per object motion blur is great. It's exactly how we percieve fast moving objects near us IRL. However heavy constant camera motion blur is an acquired taste and I'd rarely ever use it.
>vignette
Sometimes the visual presentation is just more pleasing and easy on the eyes if the the barrier between screen and monitor bezel is gradual instead of sudden. Vignette used as an effect can also be cool, like adding a red haze around the edges of the screen when you're under the effect of a red powerup.
>depth of field
Context-dependent. Constant depth of field during normal gameplay is a bad idea, but depth of field when you're locked in dialogue with an NPC during an important conversation is completely fine.

People love to just turn all of this off because they feel like it's getting in the way of the game simulation. But there are games when having post-processing effects on is the intended look, and you get something flat-looking without them.