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 Revolution Girl Style Now colorway with the Most Basic of Mitts pattern (available now).
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.