When do you use black acrylic paint out of the tube?

The most appropriate time to use the black paint out of the tube is to determine if the painting is going to be warm or cool and then go from there. I prefer to mix my black paint but if I do use it out straight of a tube I find that is best for abstracts or silhouette. If you don't use black paint correctly it can throw the entire painting off especially if you are going for a natural realistic painting.