In addition to being lawful, the processing of personal data must be fair. The fairness of the processing is essentially linked to the idea that individuals must be aware of the fact that their personal data will be processed, including how the data will be collected, kept, and used, to allow them to make an informed decision about whether they agree with such processing and to enable them to exercise their data protection rights.
When collecting your consent, organizations use a privacy notice to comply with this fairness requirement.