I debated this a while ago.
There are skills that can only be practiced and perfected alone. This I guess applies to any skills - dribbling, passing, shooting. Although you can do these in a game, I think it's best not to rely on just games to develop these aspects, as in a training environment, with cones, a wall, and of cause structure, you can get both more quality, and quantity.
But then playing pick-up games develops unteachable things like vision, composure, and decision-making.
a good mix of both is best!