I might be a bit cynical ( oh really!), but I figure a lot of what the can says is for the lawyers and deniability for the mfr. .
They ( not just Behr, all of them) say don't add stuff because they have no control, and if a problem happens then it is always the painters fault. Which is what will happen no matter.
So I figure out what works best for me, and know I'm not calling any rep to back me up.
But each paint works different, so you have to learn that paint.
And another thing I was thinking about- rMicheal is in humid and hot NC, Jake , although now is up freezing with me, cut his chops in the desert of Lost Wages, and here I am in the frozen tundra of MN. Heat and humidity of the day you are working, or inside is there AC, are the radiators hot, etc, all change the equation of what will help.
That's where a knowledgeable painter who knows the product they are working with is the key. And why we all have preferences because we find the product that fits what we are doing .