Verification is the process of ensuring that objective evidence are present and that the specific requirements are met. This process is usually done by inspections, tests, and in some instances analysis. I agree with merzkrashed that verification reduces commercial risks, risks to the users, and the costs of meeting the regulatory requirements. To add on these points, verification process ensures that design errors are detected early, and thus can be attended to before they become major. This early detection reduces potential failure in the field, which could impact on the health of the patient and even damage the reputation of the company.
In my opinion, having a design verification plan would greatly improve the verification process. This plan, therefore, ought to be developed early, not just before the verification process starts because it will be too late by then.