I would say that NB-MED guidance documents are the most useful to follow. The notified bodies have the power to inspect devices and can lead to a suspension or halted sale of the product. This can cost a company a great deal of money, not only modifying the product to make it up to standard, but also in loss of time, product, and manufacturing. To further support, competent authority guidance documents are written by competent authorities, applicable to individual countries. Oftentimes, competent authorities will follow the decision of the notified bodies and this can further apply to a MEDDEV guidance document.