This article is for the use of some brushes not all of them.
It is necessary to know our materials after several uses, we do not paint with new brushes all the time, the brushes adopt a certain characteristic over time, and that is important for us know how we can get the best form them, for example I have achieved really nice effects when painting hair but I got it only with a certain brand of brushes and after using them for a while, their hair were slightly opened, that is to say that it was a old brush and could not recover its natural form due to the constant use, but in this precise state achieved I get the best blending effects in the hair that could not achieve it with new brand brushes, that is why I keep some old brushes for certain aspects of a painting, just when they arrive at a proper worn state I separate them, one for hair, another to fade, another to create Effects of porosity, another to rub the paint and a few more.
So learn to separate your used brushes and see what effects you could achieve with them, try on a portrait, hair, cloth, flowers, to make shrubs, etc.
Of course if your brushes are so used that it is impósible to do nothing with them, that is when you trow them away.
Here some of my brushes and what I use them for.