You need someone to inspect a complicated problem, but you cannot personally test every specialist's knowledge. A credential lets another institution's assessment travel with the person. Instead of beginning from nothing, you can ask what the credential represents and whether its issuer is trustworthy.
A qualification usually connects assessment, stated learning outcomes, and an awarding body. That relationship matters more than the visual impressiveness of a certificate. Completing a course, demonstrating a skill, and receiving permission to practice are different claims.
A chain of trust
Imagine a training organization issuing a credential for bicycle maintenance. The credential is useful to a repair workshop if it communicates which tasks were assessed and at what standard. A certificate of attendance would establish a narrower fact than a practical examination, even if the two documents looked similar.
The workshop is relying on several links: the assessment must test relevant work, the issuer must apply it credibly, and the credential must belong to the person presenting it. Weakness anywhere in that chain reduces what the signal can support.
The signal and the work
Credentials can make expertise easier to recognize across unfamiliar networks. They can also become barriers when a hiring process treats possession of a particular document as the only possible evidence of ability. Someone who learned elsewhere may be capable but illegible to the system.
The distinction is between evidence and substitution. A credential can provide useful evidence about a defined achievement. It cannot substitute indefinitely for attention to what the holder can actually do, especially as tasks and circumstances change.