I find that CA can sometimes make highlights softer and also hides a bit of aliasing. Should be used in tiny amounts though.
Vignette can sometimes make an image more appealing by giving it a little more pop, it's often added in post to photos and movies because it can make an otherwise flat image more.. interesting.
A think a lot of people who hate these effects are bothered more by what they 'represent' than what they look like. They can both be attributed to low quality equipment, lens or display. Fake CA makes it look like your TV's grilles are not properly aligned and vignette is a thing low quality lens and old CRT TVs suffered from, so I can understand people who invested in their setup being somewhat pissed at anything hiding their games 1:1 pixel exact fidelity.
As usual, there's nothing inherently bad about either, and as usual, overuse or gratuitous use is always bad
Agreed. I think most post processing effects can be done tastefully. They're very underrated on NeoGAF.
Of course, abusing them can ruin the look of a game, but many games get it right. Personally, I'd say Bloodborne looks good with CA.