Wow! I'm an oil painter, and watercolor painter, but when someone once asked what my most important tool was for performing my art, without thinking, I stated "My digital camera, and Photoshop".
My computer is so important to my art, I don't know what I'd do without it.
Where to begin........???
I teach an oil painting class, and I select realistic color images of scenery, and crop, color correct, modify, grid a grayscaled version, and then I print them out in mass on my printer.
Whenever I take a digital photo from which I want to paint, I run it into Photoshop, I crop it, I size it, I proportion it, I color-correct it, I grid it, and print it out as reference images--both full-color, and grayscaled.
When I paint a portrait, I use what I call a "progressive focus" method, and this involves printing out at least 3 reference images....a normal, sharp-focus print, a semi-blurred one, and a greatly-blurred one. I use gaussian blurs in Photoshop. I print them out and I begin my painting by using the greatly-blurred one first--sometimes placing it upside down to begin painting.
I once had to exactly duplicate (as close as possible) a watercolor painting that I had painted a dozen years ago, and sold. I had absolutely no version of my original reference photo(s). What did I do? I used the old, digital file of my first watercolor painting (the one that I sold), blew it up to the final size in Photoshop, tiled it into several pieces, and printed those pieces out. I pieced them together, transfered the image to a new watercolor paper, by tracing, and used the color printout as my reference image.
As recent as my last painting, I wanted to place a figure in a landscape photo that I wanted to use as a reference image. I grabbed a figure off the internet, flopped it, sized it, rotated it, and placed it in the scene. I printed it off, and used the composite as my reference photo.
When doing a portrait from a digital photo, I often select "key colors" from the digital image, in Photoshop, and call them out, placing them in random areas on the margin of the photo. This allows for super-easy mixing-to-match of these key colors.
When I once was doing a commission, I actually showed the client via e-mail, a before-and after file of some changes that I had made. This saved me a trip to the client, carrying a wet painting.
Gosh, where do you want me to stop? These are only a few, scattered incidents that I can think of off the top of my head. My computer is absolutely essential to my creation of paintings. I did not even mention the fact that I have gained most of my knowledge of painting (glazing methods, painterly styles, mediums, paint, brushes, varnishes, composition, marketing, etc., etc.) from my computer, complete with digital examples on my computer monitor.
This forum has a Reference Image Library, which furnishes free images, from which I actually painted some of my most successful paintings.
I watch the works-in-progress of others, and learn from them. This was not possible without my computer.
Computer Applications for Learning Art? They are, indeed, infinite!