A: Putting recyclables in a bag causes a lot of problems for the recycling facility. Keeping the material loose allows the staff and equipment to process it faster, and more safely. Bags are also one of the worst "tanglers" within the facility, getting caught and tangled in sorting equipment. Additionally, if material is in a black trash bag, the sorters will assume (usually correctly) that the contents are trash, and will send them to the landfill.
Another common mistake is sending mixed materials, or non-like materials inside one another. For example, a cardboard box full of packing foam or bubble wrap makes it very difficult to process the cardboard, and the foam and stretchy plastic are two of our worst contaminants. Cardboard should be flattened, with the packing contents removed. Plastic bags and other tanglers, food residue and Styrofoam should not go in the recycling.