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: Fruitcake Old Ale
Primary: 15 Min Pale Ale (Waimea hops), Unoriginal clone (hoppy session mead)
Secondary: Why do I keep this line here...?
Bulk Aging: Simple Cyser '15, Cocobochet, Wild Cider (2014 & 2015)
Planned: So many ideas, not enough time to brew them....