Make sure you check out *staggered* nutrient additions, if you haven't already. I don't know about the others, but I usually think about adding acid blend to melomels (fruit meads) primarily...I've never bothered with any other types. It's definitely to taste, and I'd agree that it's best to wait until near bottling rather than putting it in primarily. I've put it in at the beginning before, and I've made mead...my mead has gotten better over time, and delaying the acid additions is just one of many things I've learned/done differently, so I don't know scientifically what effect it has one way to the other, but it makes sense to add it later...
Packaged: Simple Cyser '14 (Nelson Sauvin Dry Hopped!), Spiced Cider, Spur of the Moment Graff
Primary: 15 Minute APA, Simple Cyser '15
Secondary: Why do I keep this line here...?
Bulk Aging: Cocobochet, Wild Cider (2014 & 2015)
Planned: Fruitcake Old Ale, Not Just for Breakfast Stout. Otherwise, so many ideas, not enough time to brew them....