Chromatic aberration
We've talked about the camera conceit that's responsible for many of these effects. Now imagine that you're not just a camera, but a broken rubbish old camera!
Say hello to chromatic aberration. This happens in low quality or old cameras with warped lenses that can't focus colours to a precise point. The result is a a multicoloured blurring around the edges of objects, marked by a red/green/blue separation.
If a camera started doing that, you might throw it in the bin, but this undesirable and ugly effect is increasingly simulated in games. It ruins meticulously crafted environments by fraying detailed lines into coloured smudges and, like any camera effect, adds an extra layer of abstraction between you and the game world. Instead of being a soldier saving the president, you're participating in a movie about a soldier saving the president. There's a subtle difference there that takes you out of the story.