Applying cornerbead on an outside corner of your diy drywall project is to complete the job. No job is done until the paper work has been finished. Unlike drywall work, no job is complete until the cornerbead has been applied. Mudded and sanded, first the actual metal or plastic piece of 8′or 10′ foot corner cap, gets screwed or nailed over the drywall and into the framing IE wall, ceiling soffit rim etc. With a fastener every 6″ or so hold this cornerbead down and tight to the face of your drywall. In essence a phase of diy drywall is the application of any metal around the rough edge of the drywall, for the mud to be held and finalizing a finish product. Whether going square or bullnosed diy drywall cannot be complete without the cornerbead.