Do you realize that your marker and pencil strokes are physically different when you work on different surfaces?
Let's say you start out coloring at your crafting desk, then you set the project aside for a few days. When you resume coloring, you are in front of the television using a large atlas as a lap table. The next day, you finish your coloring out on the back deck at your patio table.
Each surface you encounter changes the quality of the lines you make. Check out this quick experiment, four lines each time with the same colored pencil:
Check out the skips that happened when I went over just a slight scratch in my dining room table. It's not even a noticeable scratch and yet my pencil sure found it! Tell me true, how many of you have found a gash in your table the hard way, like right in the middle of a Saturated Canary face after you spent four hours on the hair?
Ugh, just the thought of that makes me sick.
When you use an art board, you can work in the car, in the bedroom, or in the shower without the change of location being evident in your coloring.