Why use professional paints when student grade paints are so much cheaper?
They are cheaper and at face value it appears that you would save a lot of money. But what does student grade mean? Simply put it means there are fillers mixed in the paint so there is less pigment which equals less money for you to put out, but the cost is a much lower quality of paint.
You might say, so what? Who will know the difference?
You, the artist, will know the difference because it will take you a good while to mix your paint to get the right colors since it is so "watered down" with fillers.
An experiment you can do to see the real difference between student versus professional grade paints is to take a tube of student paint and a tube of identical color professional grade paint and add some white to each of the colors.
You will quickly see that the professional color keeps the true color, while the student grade totally loses the color. It's kind of a washed out color. This means you have to add more and more and more of the color to achieve the same results as the professional grade paint.
Not only is it a fabulous waste of time, but it will take a lot of the cheaper paint to achieve the same color because it has less pigment in it, and will wind up costing you not only time, but money.
Moral of the story? Get the best paint you can afford to save time and money and a big 'ol headache in the end.
P.S. If the label says "hue" it is student grade. It the label says "permanent" it is a color with lots of pigment or a professional grade. Although sometimes you will see a student grade of alizarin crimson that says permanent. This is because it is such a strong color that it can usually hold its own whether synthetic or permanent.