Why do you layer paint on a painting? What is the point?

Question:

Why do you layer paint on a painting? What is the point?

Best Answer - Chosen by Asker: With oils you layer paint to achieve better definitions of value, texture and shadow. Some paintings are even layered to the extent of actually having texture on the canvas, like impasto oils. The same can be done with acrylics. You layer with water colors because they are typically used so lightly and washed out. You layer colors on top of eachother with different saturations of color for the same reasons with oils, just a different look because they are so thin.