When you need a prescription or over-the-counter medication, you have to put your trust in the manufacturer and the government that it is safe and will not harm you. While nobody can protect you completely from side effects or adverse reactions, there are measures in place to ensure there is no intentional harm due to manufacturing issues. These are called good manufacturing practices and are established by the Federal Food and Drug Administration.
CGMs are important because you have no way as a consumer to know if a drug is out of date or has otherwise gone bad. In addition, they protect you from getting an incorrect medication because you cannot tell if a drug is the correct one until you experience its effects.
CGMs are a safeguard to ensure you are not getting bad drugs. Specifically, CGMs help to monitor the manufacturing and design of medications. They also help to ensure proper identification and labeling, so you are not getting a medication that you think is one thing but is really something else. CGMs prevent issues with mistakes and mix ups, such as improper identification of a drug or dispensing of the incorrect medication under a specified dosage.
CGMs are not meant to be a complete control system, though. They are simply the minimum requirements. Manufacturers are expected to have their own regulations in place. It is only through proper regulation that you can be kept safe and trust that when you buy an FDA regulated medication that you are getting exactly what you expect. This information is only intended to educate and should not be interpreted as legal advice.