The quality plan or quality manual of a company shows the commitments of the company to quality and compliance. Upper management has executive responsibility. Some companies adopt clauses written within ISO13485:2016 to show compliance. The Quality Plan is designed to monitor, maintain and control the processes and to drive and sustain the continuous quality improvement of the products. You need a team of cross-functional members to carry out the actions associated with the quality plan. So to answer merzkrashed’s question, yes the quality plan is essential to have.