How does the use of ISO-8859-1 affect website indexing by search engines like Google?

Using ISO-8859-1 encoding can negatively affect website indexing by search engines like Google because it does not support all special characters commonly used on the web. To ensure proper indexing, it is recommended to use UTF-8 encoding which supports a wider range of characters.

header('Content-Type: text/html; charset=utf-8');