As a clean freak - not a neat freak - those are two completely different things! I am "clean" but not necessary neat and tidy, quite the contrary actually. I clean my brushes at least once per week, if I had the time, I would want to clean it after every use.
After two weeks, your used make up brushes (especially foundation brushes and sponges) would've sprouted 15 times more bacteria than a public loo. No joke, this was on a science channel, I don't believe a lot of things on TV.. but this I do.
How often do you clean your brushes?