The 'legitimate interest' basis (Article 6(1)(f) AVG) functions within the AVG as a so-called residual basis for lawful personal data processing. The standard explanation offers a concise explanation of this basis, which includes examples of legitimate interests.
A processing of personal data is always an interference with the fundamental right to the protection of personal data. As a result, any processing is in principle unlawful. But the processing of personal data is necessary in many cases. That is why the General Data Protection Regulation (AVG) provides a legal basis for processing personal data anyway. This basis consists of six bases. Can a controller rely on at least one of these six bases? Then the processing is still lawful (if it concerns 'ordinary' personal data, so no special or criminal data - extra strict rules apply to these).
Read more: Standards explanation basis 'legitimate interest'.