Makeup brushes are expensive. When you get a good one, you want to take care of it.
After washing makeup brushes, an important part is drying them. Seems simple enough. If you stand thee brushes up in a cup to dry.. not only will the bristles fall over and you will lose the shape of the bristles, the water will drip into the base of the brush.
Sounds harmless enough – water evaporates right? Yes, but, it can start molding in the base of the brush, if you let the water drip into the base of the brush. Not only do you risk losing the shape of the bristles, but bacteria, mold and other gunk can build up and thrive with the water settling in the base of the brush. Other things can happen too, but the important thing is, taking care of the brushes means retaining the shape of the bristles after cleaning them as well as drying them upside down . Your brushes will last longer drying them upside down and an over the door towel hanger works great!
Personally, I would rather wipe a few drips off the floor than dish out the money for new brushes every few months!
It can also work for art brushes ;)