Well, I have learned in the past year for many things there are multiple opinions and you will see them on this site.
There are also things that are tried and true and many of us have learned the hard way.
Most of the opinions like your angel example or mixing of certain livestock or waiting a period of time for corals, etc are based on experience and common knowledge gained through this experience. There are always a few exception where something works for one, but for most will not.
We are dealing with animals and like any other animal, every individual is different and there are exceptions to most rules. That is why most of us will encourage you to read through mulitple post, books and article and make you own educated decisions.
Its not the easiest hobby in the world, there are no clear cut answers to many aspect of this hobby. You just need to study, get you hands wet (so to speak), listen to different opinion and base you game plan on what you conclude to be the best info. Do your homework on your animals, and qt
everything (that most of us will agree on) and you will have sucess in this hobby.
And don't be afraid to challange people on their advise. Healthy debate benefits us all.
Thanks for the post, its a good one!!