Red-tape or very useful?
Simply put, a calibration certificate is proof that you have had your instrumentation recently calibrated and that your equipment was performing as expected at the time of testing. But a calibration certificate can be much more than that. It also gives you known errors so that you can safely adjust processes or make allowances for errors on that instrument. It can also be a sign to customers that you take your quality assurance processes seriously. It gives you assurance that your processes are running correctly and your products are being produced correctly. It can also provide assurance that you are selling products at the correct weight and are not underselling. It can also ensure you are not overselling products by weight and giving away profits.
If your business is selling goods by weight, your scales will need to be M class verified and regularly calibrated. This will ensure that you are complying with trading standards laws.
Usually, a company with a quality management system is obliged to calibrate their equipment regularly and hold copies of their calibration certificates.