I always have several going on at once. I have a project I'm doing w/friends & we meet usually once a week. Also I can get bored if I'm doing a project with the same block repeated over & over - & of course have to interrupt everything if I need to make a gift.
But as the original poser said, I can't work in clutter. So any project not finished is kept aside, all elements together in a tote - helps keep things neat.