Doodling is fun. It is also a bit meditative as you concentrate on small tasks much more than you realise you might and this allows your mind to be still.
I think it also makes you more comfortable with a pencil and builds up muscle memory.
These doodles can also give you inspiration for textures in drawing. In the example above there is hair, snow, tiles, road, curtain, crop circles, metal flooring, bricks, Charlie Brown clothes... lots of different uses for doodles.
