Life gets busy. I know that when I got up this morning at 5:20 am (eesh) the last thing on my mind was makeup brushes, but let me tell you what, they came in handy.
These days I use makeup brushes for pretty much everything (save my Studio Fix application) that involves makeup. I use a brush to conceal my blemishes and to apply my foundation (whether it be the Bare Minerals I use now, or the liquid foundation I used to use), to apply blush, and when I have the time, to apply eyeshadow. It may seem superfluous to have so many makeup brushes, but I can attest to the fact that they have been a lifesaver.
First off, let's discuss why it's advantageous to use makeup brushes.
One of the most integral parts of makeup application is to enhance your face in a natural way, rather than appearing as if you have a bad tan on top of seven layers of cheap makeup. There are instances where you can play up your features with eyeshadow, eyeliner and lipstick where it's obvious you're wearing makeup, but the point is to make it look like it's a seamless extension or enhancement of your face. Makeup brushes, then, become vital because they aid in the application process of your makeup.
Brushes give you more control over the quantity of makeup you apply. As I recommended in my red lipstick post, a lip brush is a great avenue to pursue when applying a bright red lipstick, because you have more control over the amount of lipstick that is dispersed. The same applies for foundation, blush and eyeshadow.
Even if you have flawless skin, it is always wise to apply some sort of foundation (even if it's just a tinted moisturizer or something with minimal coverage) in order to even the tone of your skin. And the point of foundation is to appear as if you're not wearing it. When you use a makeup brush that is specifically designed for this purpose, you have a better chance of evenly applying your base makeup, thereby creating a natural rather than a cakey look.
Similarly, when you apply your blush, it should be a hint of color that enhances your face's natural glow, rather than being a 1980's hot pink streak across your cheeks. A proper blush brush helps distribute the rogue in a way that does so; so the apples of your cheeks look delightfully natural, and not Bozo the Clown-ish.
Eyeshadow can be tricky to apply, for it can easily crease or bleed. Using a eyeshadow brush, and tapping off excess shadow can ensure an even application that reduces the risk of creasing/bleeding because there is not excess makeup on the brush. This also mitigates the chunky eyeshadow look that plagues every eight year old that experiments with mom's makeup.
It is important to purchase high quality makeup brushes because they last longer and apply makeup better. Also, I would invest in a brush cleaner (this one is my favorite) so that you can regularly clean your brushes and preserve their life. I cashed in a few years ago when MAC was selling a mini-brush set for a steal (their brushes can get quite pricey). The only difference between my brushes and the full size brushes is their length. And, the set came with a darling case to hold them in. So keep your eyes peeled for deals like that. Below are the brushes that I believe are critical for basic makeup application. Even if you get them one by one over a period of time, it will be worth it. Trust me on this one.