Almost all digital painters know what speed painting is and I am sure that speed painting is even practiced by other painters as well. There are no real rules when it comes to digital speed painting except do it fast as possible. A speed painting can take from anywhere from 15 minutes to paint to 2 hours, although some people like to take as long as 3 hours. There are plenty of arguments out there what the max time for a speed painting, but in reality --- it is all relative to the size or complexity of composition of the painting. Some ask why do a speed painting other than the reason for showing off. Well there are a variety of reasons. First off, time is money and if you can create a quite composition in as little as time possible then you can save time and earn more money. Another good reason to do speed painting is it is intense training designed to sharpen the compositional skills of the artist. Being able to speed paint is also vital for visual development in a variety of industries because visual development is about getting out images fast in order to communicate a visual idea that we as artists have in our heads. Lastly from my own experience some of my best portraits and other paintings have started off as a speed painting but which I just moved forward on. The reason I believe this to be so is because I am not thinking of what I want or need to do but instead I react and counter react as a speed painting I am doing develops. Also when I am working on a speed painting I usually like having some kind of loose photo reference(s) as this allows me to react without having to think to much.