Good for keeping your hands warm and your fingers free to do things. I've heard they are also good for doing fancy penwork while protecting your hands and paper.
These were made from 4 Plies of the Apocalypse with the Starry Starry Night colorway with the Power Up chart and the Most Basic of Mitts pattern (available now if you'd like to make your own).
Fingerless mitts made in one size fits many. I wear typically medium/small women's size 7.5 gloves and these are pictured on my hand.