Well, the correct question should be [Why SHOULD I use a makeup artist?].
Although using a professional makeup artist isn’t required, it’s highly recommended, especially for women. Perhaps you are very skilled at doing your own makeup for day to day use. However, doing makeup for being in front of a camera or video is a bit different. The makeup artist also stays for the entire shoot to do minor touch-ups or hair fixes and to just generally keep you looking your best during your shoot. Your makeup should look fresh and natural looking and should accentuate your features. It should not make you LOOK like you are made up. You should look like you look on your best day! When you show up for your shoot you should already have your hair done up as if you were going out.